Slit-like Cavity Research Articles

Comparative evaluation of transscleral laser exposure in anatomical experiment

This study comparatively analyzed the morphology of eye tissues after laser exposure using the latest generation of transscleral laser techniques - micropulse transscleral cyclophotocoagulation (MP-TSCPC) and laser activation of scleral hydropermeability (LASH) - in an anatomical experiment. The study used pulsed-periodic radiation of an Er-glass fiber laser (λ=1.56 μm) and radiation of a diode laser (λ=0.81 μm) in the micropulse mode. A comparative morphological evaluation of histological preparations of target scleral and ciliary body (CB) tissues was performed with the study of laser-induced changes occurring after LASH and MP-TSCPC. The study of histological preparations obtained after MP-TSCPC and LASH did not reveal any noticeable signs of an inflammatory reaction or significant destructive changes. There were no signs of pronounced coagulative changes in the form of disorganization of connective and muscle tissue in the exposure area. At the same time, MP-TSCPC was accompanied by thinning and discontinuity of the CB pigment epithelium in the projection of its flat part and expansion of the gaps between the anterior connective tissue fibers fixing the CB to the sclera, which is likely a factor contributing to uveoscleral outflow. After LASH, in the irradiated areas at the level of the outer layers of the sclera (¾ of its thickness) located in the projection of the flat part of the ciliary body, multiple slit-like cavities and enlargements (stretching) of interfiber spaces were revealed with simultaneous compaction of the inner part of the sclera (¼ of its thickness). The identified morphological changes may indicate certain differences in the mechanisms of intraocular pressure (IOP) reduction after MP-TSCPC and LASH. The results of this study suggest that the enhancement of uveoscleral outflow of intraocular fluid and the hypotensive effect after MP-TSCPC may be associated with laser-induced expansion of the interspaces between the anterior connective tissue fibers of the CB in the suprachoroidal space. With LASH, the possible mechanism of lowering IOP may be related rather to an increase in transscleral filtration due to the appearance of slit-like interfiber spaces in the sclera, caused by local contraction of scleral fibers in the area of laser exposure. The absence of pronounced destructive changes at the histological level indicates the gentle nature of both laser techniques and the possibility of expanding the indications for the use of LASH in the treatment of glaucoma, including at its earlier stages.

Structural insights into AtABCG25, an angiosperm-specific abscisic acid exporter

Cellular hormone homeostasis is essential for precise spatial and temporal signaling responses and plant fitness. Abscisic acid (ABA) plays pivotal roles in orchestrating various developmental and stress responses and confers fitness benefits over ecological and evolutionary timescales in terrestrial plants. Cellular ABA level is regulated by complex processes, including biosynthesis, catabolism, and transport. AtABCG25 is the first ABA exporter identified through genetic screening and affects diverse ABA responses. Resolving the structural basis of ABA export by ABCG25 is critical for further manipulations of ABA homeostasis and plant fitness. We used cryo-electron microscopy to elucidate the structural dynamics of AtABCG25 and successfully characterized different states, including apo AtABCG25, ABA-bound AtABCG25, and ATP-bound AtABCG25 (E232Q). Notably, AtABCG25 forms a homodimer that features a deep, slit-like cavity in the transmembrane domain, and we precisely characterized the critical residues in the cavity where ABA binds. ATP binding triggers closure of the nucleotide-binding domains and conformational transitions in the transmembrane domains. We show that AtABCG25 belongs to a conserved ABCG subfamily that originated during the evolution of angiosperms. This subfamily neofunctionalized to regulate seed germination via the endosperm, in concert with the evolution of this angiosperm-specific, embryo-nourishing tissue. Collectively, these findings provide valuable insights into the intricate substrate recognition and transport mechanisms of the ABA exporter AtABCG25, paving the way for genetic manipulation of ABA homeostasis and plant fitness.

Elastification of the arterial wall by high-intensity low-frequency ultrasound

A significant increase in the elasticity of the femoropopliteal artery segments in vitro was found as a result of the action of cavitation generated by powerful low-frequency (24–26 kHz) ultrasound introduced into the vessel by a flexible waveguide. The vessel elasticity was evaluated both by the deflection under the action of an external force and by the degree of its expansion vasodilatation by the internal pressure created by the expanding balloon. The possibility of achieving a more than two-fold decrease in the vascular wall elasticity modulus after 30-s exposure to an ultrasound intensity of 31 W/cm2 was shown. It has been established that at the 10 μm amplitude of ultrasonic vibrations, vascular wall damage occurs in the form of small foci of detachment and rupture of the intima accompanied by delamination in the media layer, when polymorphic slit-like cavities are formed with an increase in the amplitude of oscillations above 23 μm.

Do Large Herbivores Have an Important Role in Initiating Tree Cavities Used by Hole-Nesting Birds in European Forests?

Tree cavities are an essential resource for cavity-dwelling mammals, birds, invertebrates and fungi, and so are important for maintaining forest biodiversity. In North American forests, woodpeckers (Picidae) play a keystone role in cavity creation by excavating holes. However, in European forests many hole-nesting songbirds rely on non-excavated cavities that are formed by fungal decay and compartmentalization after tree damage. Several factors are recognised in initiating non-excavated cavities that are used by hole-nesting birds, including loss of a tree branch or stem breakage, but this topic is poorly studied. Here, we propose that bark stripping by large herbivores (e.g. Red Deer Cervus elaphus and European Bison Bison bonasus) could be another important, and previously overlooked, mechanism for initiating tree cavities that are used by hole-nesting birds. We suggest that, after the initial damage from herbivore bark-stripping, fungal decay can create specific elongated, slit-like cavities, which are particularly important as nest sites for some common forest songbirds. We outline this idea using original observations and evidence from the literature, primarily from the primeval forest in Poland's Białowieża National Park. We also use studies from elsewhere in Europe to show a generally low usage of slit cavities by birds where large herbivores are scarce or absent. We suggest that restoring such animals in European forests could help to restore the abundance and diversity of the tree cavity resource for hole-dwelling species. We encourage future research to investigate this proposal of large herbivores being important agents of tree cavity formation that could enhance biodiversity.

The impact of the adsorbent energy heterogeneities by multidimensional-multicomponent PC-SAFT-DFT

Over the past few decades, the classical density functional theory (cDFT) models have gained importance in modeling inhomogeneous fluids. Notably, adsorption databases produced by non-local DFT (NLDFT), quenched solid DFT (QSDFT) and 2D-NLDFT approaches are used in different characterization methodologies to recover the pore size distribution (PSD) for a various nanoporous materials. This family of models has a much lower computational cost when compared to molecular simulation. However, it lacks formulations that use DFT for multidimensional-multicomponent systems with heterogeneous solids. In addition to the complexity of representing the interactions between confined molecules and their confined mixtures, it is challenging to represent surface heterogeneities. Here we study materials with equivalent external potential but presenting energy heterogeneities varying throughout the material using a multidimensional classical DFT approach consistent with the SAFT equation of state. For this purpose, we applied three external potentials to model three types of slit-like cavities. Among them, a classical slit-like pore was generated, in which the energy sites did not vary along with the material. In the other two cavities, the energy sites could vary along the cavity, simulating a cavity in which the external potential varies bidimensionally. Finally, we evaluate the effect of the energy heterogeneity of these cavities on the adsorption of Ar and Kr and their mixing. The results show that local heterogeneities can alter the shape of isotherm curves and adsorption selectivities. Solids with heterogeneity showed higher selectivity but lower capacity.

Температурная динамика карбонизации хлопковых волокон микроволновым излучением на воздухе

Spectral pyrometry was used to determine the dynamics of microwave heating in air of samples (3 g samples) of cotton fibers pretreated with 2, 5, 7, and 10 % aqueous H3PO4 solution. Microwave heating was carried out in an open quartz reactor. The processing of the recorded radiation spectra and the calculation of the temperature were carried out using the “Spectral pyrometry” program. It has been established that the graph of the change in the temperature of the sample during heating has three characteristic regions — low-temperature, the region of unstable temperature, and the region of temperature stabilization. In the low-temperature region, free moisture is removed from the sample. The region of unstable temperature is associated with the process of cellulose combustion, which begins after the end of moisture evaporation at a temperature above 600 K. Under the influence of microwave radiation, all chemical processes intensify in the sample. Video filming during microwave heating showed that in the process of irradiation, sinuous slit-like cavities are formed on the surface of the sample, inside which electrical discharges and ignitions form “hot spots”, from which heat spreads to the entire volume of the sample and additionally heats it, which leads to significant temperature fluctuations. The combustion process continues until all the material is carbonized. After that, a relative stabilization of the temperature occurs, the value of which lies in the range of 1000 – 1200 K. It has been established that the higher the concentration of the H3PO4 solution used for pretreatment of the samples, the lower their temperature in the given area. It has been shown that the carbonization process begins in 70 – 75 s from the start of heating in the local areas of the sample. The results of comparative studies of the structure and elemental composition of samples before and after microwave exposure are presented. It is shown that after 180 s of heating, the fibers become significantly thinner, while maintaining integrity along the length. Carbonized fibers contain a significant amount of phosphorus, the concentration of which is maximum in the outer layers of the sample and is 15 – 20 %. The total weight loss of the samples depends on the concentration of the H3PO4 solution used to pre-impregnate the samples and ranges from 94 % for 2 % H3PO4 to 82 % for 10 % H3PO4.

Prospective Follow-up of Intramedullary Slitlike Cavities: A Consecutive Series of 48 Patients.

Object: Predicting whether intramedullary slitlike cavity (SC) will worsen over time or remain stable is an outstanding clinical challenge. The aim of this study was to identify early features of SC (clinical and magnetic resonance imaging [MRI] findings).Methods: We prospectively included all patients referred to our institution following the discovery of a SC and divided them in two groups: typical SC (defined as a cavity spanning fewer than three vertebrae, not enlarging the spinal cord, and located at the midline between the anterior third and posterior two-thirds of the spinal cord) or atypical SC (all others). Clinical evolution and changes in MRI features were evaluated during follow-up. In some patients, diffusion tensor imaging was performed and cervical cord cross-sectional area was analyzed.Results: A total of 48 consecutive patients were included in the study. The mean follow-up was 58 months. Of the seven patients presenting with deficits at first consultation, two worsened and five remained stable. Of the 41 patients without deficits, seven worsened and 34 remained stable. None of the patients developed severe motor deficits or experienced enlargement of the cavity; 7% of patients who presented with typical SC worsened compared with 35% with atypical SC. The negative predictive value was 0.93 (P = 0.02).Conclusion: Most patients remained stable and a subset of patients developed minor motor deficits. For clinical management, we propose surveillance of patients with a typical SC and close follow-up of those with an atypical SC and/or presenting with deficits.

A Microtomographic Osteology of the Supraoccipital Hook of Nurseryfish,Kurtus gulliveri(Perciformes: Kurtidae)

The Nurseryfish, Kurtus gulliveri, is known for “forehead brooding” parental care behavior in which the adult male carries the egg mass on a hook that overhangs the “forehead” region. This hook is derived from the supraoccipital bone, and it has been suggested to be formed through absorption rather than growth of the supraoccipital crest (SOC). Here we employed X-ray microtomography to investigate the neurocranium with focus on occurrence of the supraoccipital hook in a series of specimens from postflexion larva to adult male and female (10–200 mm SL). A slit-like cavity filled with soft tissue but not spongy bony tissue was revealed in the SOC in all examined specimens except the two smallest larvae (<15 mm SL), thus the cavity appears in the late postflexion-stage. The SOC can be divided into three parts from anterior to posterior in juveniles and adult females by reference to the cavity. 1. The crest rostrum is the most anterior end of the supraoccipital, and it increases in height with a sloped dorsal...

Maxillary sinus atelectasis in a wild born gibbon (Hylobates moloch)

In a mixed sex sample of ten adult gibbon (Hylobates moloch) skulls, one cranium of a male with maxillary sinus atelectasis of the left side was identified. While external inspection revealed a slight drop of the left orbital floor, serial coronal computer tomography (CT) scans show characteristic changes of the left maxillary sinus and its surrounding structures. In addition to the sunken orbital floor, radiological features of the specimen include an inward bowing of the medial sinus wall, sinus opacification, and a reduction in maxillary sinus size to a slit-like cavity, which suggest a diagnosis of silent sinus syndrome. This report is the first, to our knowledge, of maxillary sinus atelectasis in a non-human primate. This finding is valuable for the understanding of the pathogenesis and etiology of maxillary sinus atelectasis. At the same time, however, paleoanthropologists and primatologists may refer to this information when dealing with the interpretation of maxillary sinus pneumatization of partially broken archaeological and fossil skulls.

Slitlike syrinx cavities: a persistent central canal.

The authors review their experience in the diagnosis and management of 32 patients with slitlike syrinx cavities. There were 18 men and 14 women with a mean age of 40 years. Presenting symptoms that prompted magnetic resonance (MR) imaging evaluation were mechanical spinal pain (13 patients), radicular pain (seven patients), paresthesia (six patients), numbness (five patients), and muscle spasm (one patient). In 12 patients neurological examination demonstrated normal status, and in the remainder only minimal sensory or motor abnormalities were found. The mean diameter of the syrinx cavity was 2 mm (range 1-5 mm), and on average it covered three vertebral levels. The cavities were limited to the cervical region in 16 patients, the thoracic in 12, and both regions in four patients. The mean follow-up time for changes in clinical condition and repeated MR imaging features were 38 and 32 months, respectively. Thirty-one patients were treated nonoperatively, and one was treated surgically. During the follow-up period clinical improvement was documented in six patients, worsened status in seven, and no change was demonstrated in the clinical status of 19 patients. None of the syrinx cavities changed in size. In 16 patients medical workup revealed alternative diagnoses that were determined to be the true causes of each patient's symptoms. Slitlike cavities likely do not represent true syringomyelia but rather remnants of the central canal detected in a small percentage of adults. Review of the authors' experience indicates that these cavities are asymptomatic and are unlikely to change in size. They can be considered an incidental finding, and in many of these patients another condition explaining the patient's symptoms may be found.

Multiple sclerosis with secondary syringomyelia: An autopsy report

We report an elderly woman with multiple sclerosis who showed an extensive cavity formation in the midthoracic cord in addition to multiple abnormal intensity signals in the central nervous system on magnetic resonance imaging (MRI). The cavity decreased in size in response to corticosteroid therapy with an improvement in neurological symptoms. The autopsy demonstrated a slit-like cavity lined with no ependymal cells on the luminal surface in the lower cervical to midthoracic cord, with circumferentially distributed demyelinative lesions, leading to the pathological diagnosis of secondary syringomyelia. In this patient a limited necrosis formed in the spinal cord might have developed into a cavity formation with edematous fluid leading to subsequent episodes of neurological exacerbation.

Band-flip and kink as novel structural motifs in α-(1→4)- d-glucose oligosaccharides. Crystal structures of cyclodeca- and cyclotetradecaamylose

Cycloamyloses (CAs) with 10 and 14 glucose units (cyclodeca- and cyclotetradecaamylose, or ι-cyclodextrin and ε-cyclodextrin, respectively) crystallize as 23.5 and 29.7 hydrates, respectively. Both crystals belong to the monoclinic space group C2, with half molecules in the asymmetric unit, the other halves being related to the first by crystallographic twofold axes. NMR and X-ray analyses show that in CA10 and CA14, two diametrically opposed glucoses are flipped ∼180°, leading to elliptical structures with narrow, slit-like cavities. In both molecules, the flipped glucoses are stabilized in orientation by intramolecular three-centered hydrogen bonds with O-3( n)–H as donor, namely O-3( n)–H⋯O-6( n+1)B and O-3( n)–H⋯O-5( n+1). The other glucoses are stabilized by O-2( n)⋯O-3( n−1) hydrogen bonds (as observed in the smaller α-, β- and γ-cyclodextrins) except at two kinks where these distances are long (3.98 and 3.39 Å, respectively). The geometry at the flip site, unusual for α- d-glucoses oligosaccharides, is similar to the one observed in the crystal structure of β- d-cellotetraose (structural model for cellulose II). In both molecules, conformations are unstrained with glucoses in 4 C 1 form. Due to their conformational pecularities, CA10 and CA14 crystal structures combine in their crystal lattice the two common packing motifs characteristic of the smaller cyclodextrins, namely parallel channels with intermolecular contacts in herringbone arrangement. Since 13C NMR chemical shifts observed with CAs and amylose in solution and solid state are similar, we anticipate the presence of band-flips and kinks in the polymer. As demonstrated by computer simulations, the band-flip’s novel structural motif occurs in (cyclo)amylose to relieve steric strain.

Marine Bakterien, VII. Enzymatische Bromierung von Pseudilinen und verwandten Heteroarylphenolen mit der Chlorperoxidase aus Streptomyces aureofacens Tü 24

Marine Bacteria, VII. – Enzymatic Bromination of Pseudilins and Related Heteroarylphenols with a Chloroperoxidase from Streptomyces aureofaciens Tü 24During the bromination of various substituted synthetic phenyl pyrroles with a chloroperoxidase from Streptomyces aureofaciens Tü 24, mixtures of bromopyrroles are obtained which are not easily accessible by chemical methods. According to the structure of the pyrroles and the kinetics of their transformation, the reaction centre of the enzyme is situated in a slitlike cavity of about 4 × 7 × 8 Ä. magnified image

MR evaluation of Chiari I malformations at 0.15 T.

Twelve patients with known or presumed Chiari I malformations and two with clinical diagnoses of multiple sclerosis were examined by magnetic resonance (MR) imaging. MR confirmed or established the diagnosis of Chiari I malformation in all 14 cases. The spin-echo technique with a short time to echo (TE = 40 msec) and a short time to recover (TR = 1000 msec) provided optimum imaging of tonsillar position, hydromyelia cavities, and cervicomedullary "kinking." Long TE (greater than 80 msec) and TR (greater than 2000 msec) increase the signal intensity of cerebrospinal fluid and may obscure the pathology. Sagittal, transaxial, and coronal images provided complementary data; sagittal and coronal views best imaged the abnormal spinal cord and tonsils, but slitlike cavities were best seen on transaxial images. Cervicomedullary kinking was found in 10 (71%) of 14 patients and in 90% of the hydromyelic patients. This high incidence suggests that in other radiologic techniques tonsillar herniation masks the kinking. Symptoms of the Chiari I malformation overlap those of demyelinating diseases and brain tumors. Our early experience suggests MR is the preferred noninvasive procedure for identifying Chiari I malformation. Moreover, the ability to portray the variable cavity morphology of hydromyelia directly offers the potential for improved shunt placement.

Histological and ultrastructural studies of secondary neurulation in mouse embryos.

The histological and ultrastructural features of secondary neurulation in C57BL/6 mouse embryos were examined as a first step in the analysis of how this process occurs in mammalian embryos. Secondary neurulation involves two major events in mouse embryos: (1) formation of the medullary rosette (9.5- to 10-day embryos) or plate (11- to 12-day embryos), and (2) cavitation. These two events occur simultaneously. The medullary rosette consists of elongated tail bud cells, radially arranged around a central lumen formed by cavitation. The secondary portion of the neural tube forms in 9.5- to 10-day embryos by progressive enlargement of the central lumen and addition (by cell recruitment or mitosis) of tail bud cells to the rosette. The medullary plate likewise consists of elongated tail bud cells, but these cells do not surround a central cavity. Instead, cells of the medullary plate extend ventrad from the basal aspect of the dorsal surface ectoderm to a slit-like cavity formed by cavitation. Formation of the secondary neural tube occurs in 11- to 12-day embryos, principally by the recruitment of more lateral and ventral tail bud cells into the medullary plate. Free cells and cellular debris are frequently encountered in the forming lumen of the secondary neural tube, but cells exhibiting signs of necrosis were absent in cavitating regions. Numerous small intercellular junctions form at the inner ( juxtaluminal ) ends of tail bud cells as the medullary rosette or plate is forming and cavitation is occurring. These observations suggest that cavitation per se (i.e., formation of a lumen) during secondary neurulation is a relatively passive phenomenon, which results principally from neighboring cells becoming polarized apicobasally and incorporated into a primitive neuroepithelium. The latter constitutes the walls of the forming secondary neural tube.

Immunohistopathology of allergic rhinitis and conditions allied.

Knowledge of nasal physiology and function is necessary for a proper comprehension of nasal symptoms; a short introduction on this topic follows. It is an important task for the nose to filter, humidify and warm the inhaled air. The shape of the nasal cavity and the structure of the nasal lining seem particularly well suited for this purpose. The narrow inlet to the airway (the internal ostium), the bend of the airflow in the nasopharynx and the slit-like cavity provide for effective sedimentation of practically all particles, larger than 10μm, and also of some smaller particles (2–3 μm).1 Foreign particles deposited in the nasal filter, contact the local immune system. The airway mucosa is equipped with a secretory IgA immune system, which may help to render deposited micro-organisms harmless,2 but also IgE producing cells are found in the mucous membrane and in the regional lymph nodes.3 Therefore, the constant sedimentation in the nose of potent allergenic substances (pollen, animal dander, house dust mite) and the consequent risk of allergic rhinitis is a price which has to be paid for nasal filtration and protection of the lower airways against unconditioned ambient air. The nose is also designed for heating and humidification of the inhaled air. Again the slitlike shape of the cavity is of decisive importance, as the intimate contact between the mucosal surface and the inhaled air is necessary for rapid supply of water and heat to the air the nasal cavity. Normally the air passes the nose at a speed of 2 m/sec.4 The numerous seromucous glands,5 some anterior serous glands6 and subepithelial capillaries of the fenestrated type7 form the basis for the supply of 500 ml water a day to the inspired air.8 The venous sinusoids seem especially designed for maintenance of a slit-like nasal cavity, so important for normal function. More than half of the nasal blood flow is shunted through an abundance of arterio-venous anastomoses.9 A comparison with hot water running in a radiator illustrates the importance of this arrangement for heating of the inspired air.

Eccentric ventricular hypertrophy in familial and sporadic instances of 46 XX, XY Turner phenotype.

This study of individuals with familial and sporadically occurring 46 XX or XY Turner phenotype documented a wide range of right- and left-sided cardiovascular abnormalities and a previously unreported eccentric hypertrophy of the left ventricle. A mother and five of her seven children had abnormal cardiovascular findings. Five had an abnormal electrocardiogram with frontal ÂQRS of -60° to ±180° and rS or rsr' in V 1 and rS, qrS, or qRS in V 5 . Catheterization demonstrated the following anomalies: coarctation of the aorta in three, valvular aortic stenosis in one, pulmonary valvular insufficiency with atrial septal defect in one, and pulmonary arterial branch stenosis in one child. All six had a similar abnormality of the left ventricle on angiocardiography. During systole and also in diastole the cavity was encroached on in its superolateral and posteroinferior aspects. Septal hypertrophy altered right ventricular contour in two. A similarly abnormal electrocardiogram and left ventricle were found in four unrelated individuals with the XX, XY Turner phenotype. Three had pulmonary stenosis; in two there was an associated septal defect. The fourth, with no associated cardiac defect, died in heart failure at 5 months of age. At necropsy she had marked eccentric biventricular hypertrophy, chiefly involving the left ventricle so that the chamber was reduced to a slitlike cavity. The hypertrophied septum bulged into the right ventricular outflow tract. A number of cardiovascular anomalies occur in familial and sporadic instances of this syndrome; eccentric ventricular hypertrophy recognizable by an electrocardiographic abnormality seems to be a distinctive cardiac lesion in the XX, XY Turner phenotype. Except for the unusual and, we believe, characteristic ECG, there was no clinical clue on physical examination or cardiac series of chest roentgenograms to suggest the presence of eccentric left ventricular hypertrophy. We recommend that selective left ventricular angiocardiography be performed when patients with the Turner phenotype undergo diagnostic cardiac catheterization, especially when the frontal ÂQRS is superiorly directed.

Cor biloculare: Case report

The heart described was unusual in that it consisted primarily of only one atrium and one ventricle with a patent ductus arteriosus. The ventricle had a rudimentary slitlike cavity in its wall, but this to all intents and purposes was nonfunctioning. This case, we feel, is a cor biloculare.

The ‘Segmentation Cavity’ of the Egg of the Frog.

ABSTRACT The egg of the frog, Rana temporaria, starts its career of segmentation as does that of Amphioxus, but after the onecelled blastula stage a delamination of cells takes place, with the result that the wall becomes multicellular. The cavity is excentrally situated, the anterior wall being thin and the posterior wall thick. The latter consists of endoderm, and while internally it is impossible to point to a distinct demarcation between ectoderm and endoderm, externally an equatorial zone is defined which marks the limits of ectoderm and endoderm, and this is emphasized when the zone becomes a ring of proliferation indicating the beginning of the activities of the blastopore. The proliferation is followed by the appearance of a dorsal groove, the dorsal lip of the blastopore. An invagination takes place, confined, however, to the dorsal aspect of the embryo, and a horizontal slit-like cavity is produced which penetrates anteriorly above the segmentation cavity and is extended posteriorly as the dorsal lip of the blastopore advances over the large cells of the yolk-plug. This cavity is the enteron, and while it is forming the original cavity, which is still called the segmentation cavity, acquires a cup shape, the anterior wall being definitely resolved into ectoderm, and the endodermal margin of the cup gradually narrows and ultimately fuses, so that the cavity becomes enclosed in endoderm. It is almost universally believed that the segmentation cavity is compressed by the expanding enteron and that it finally disappears antero-ventrally in the endoderm. But A. M. Marshall, 0, Schulze, and 0. Hertwig have all drawn attention to cases of fusion between the two cavities, cases which indicate that sometimes the segmentation cavity may become converted into the forward part of the enteron. Such have been regarded as abnormal, and upholders of the orthodox view of the procedure which takes place within the egg of the frog explain them as being due to faulty preservation or preparation. On the other hand, the accepted view is not supported by a convincing series of figures. A stage is shown which presents the segmentation cavity and the enteron. The next stage is one which displays the enteron occupying the place of the segmentation cavity and the latter as non-existent or as a small cavity of the endoderm ventral to the enteron. Even if such a change actually takes place it is plain that the subsequent excavation and thinning of the ventral and lateral walls of the endoderm restores the cavity to the enteron, and the process could be explained as a variation of that produced by an earlier fusion of the two cavities. With this in mind it may be said, to begin with, that, if the segmentation cavity sometimes produces the anterior part of the enteron and usually disappears as a cavity enclosed by endoderm, the nomenclature of the cavity is wrong and misleading.