Transverse Vessel Research Articles

Complete removal of a cavernous malformation in the dorsal pons, in contact with the expanded transpontine vein: illustrative case.

Craniotomy is required for the removal of brainstem cavernous malformations (CMs) with repeated hemorrhage, and this condition is often complicated by an accompanying developmental venous anomaly (DVA). However, a DVA of the brainstem or cerebellum with drainage penetrating the pons is an exceptional finding. A 57-year-old man presented with double vision. Computed tomography revealed progressive enlargement of the hemorrhage in the dorsal pons. Contrast-enhanced magnetic resonance angiography revealed an expanded transverse vessel penetrating the center of the pons in contact with the CM. Digital subtraction angiography revealed that the DVA, comprising the expanded transpontine vein and some cerebellar medullary veins acting as normal venous drainage, coexisted with the CM. By utilizing the angioarchitecture and intraoperative neuronavigation system data, electrophysiological mapping, and indocyanine green videoangiography, complete removal of the CM was accomplished while preserving the DVA and brain function. This study presents the intraoperative images of an expanded transpontine vein as a DVA, which has never been depicted in a live patient before, accompanied by a CM in the dorsal portion of the pons. https://thejns.org/doi/10.3171/CASE24314.

First echinoderm alpha-amylase from a tropical sea cucumber (Holothuria leucospilota): Molecular cloning, tissue distribution, cellular localization and functional production in a heterogenous E.coli system with codon optimization

Holothuria leucospilota (Echinodermata: Holothuroidea) is a widespread tropical sea cucumber with strong value for the ecological restoration of coral reefs. Therefore, some studies regarding the artificial breeding and cultivation of H. leucospilota have been undertaken recently. However, the biological functions of the digestive system of this species have not been elucidated. In this study, a cDNA coding for α-amylase, an indicator of digestive maturity in animals, was identified from H. leucospilota and designated Hl-Amy. The full-length cDNA of the Hl-Amy gene, which is 1734 bp in length with an open reading frame (ORF) of 1578 bp, encodes a 525 amino acid (a.a.) protein with a deduced molecular weight of 59.34 kDa. According to the CaZy database annotation, Hl-Amy belongs to the class of GH-H with the official nomenclature of α-amylase (EC 3.2.1.1) or 4-α-D-glucan glucanohydrolase. The Hl-Amy protein contains a signal peptide at the N-terminal followed by a functional amylase domain, which includes the catalytic activity site. The mRNA expression of Hl-Amy was abundantly exhibited in the intestine, followed by the transverse vessel with a low level, but was hardly detected in other selected tissues. During embryonic and larval development, Hl-Amy was constitutively expressed in all stages, and the highest expression level was observed in the blastula. By in situ hybridization (ISH), positive Hl-Amy signals were observed in different parts of the three different intestinal segments (foregut, midgut and hindgut). The Hl-Amy recombinant protein was generated in an E. coli system with codon optimization, which is necessary for Hl-Amy successfully expressed in this heterogenous system. The Hl-Amy recombinant protein was purified by immobilized metal ion affinity chromatography (IMAC), and its activity of starch hydrolysis was further detected. The optimal temperatures and pH for Hl-Amy recombinant protein were 55°C and 6.0, respectively, with an activity of 62.2 U/mg. In summary, this current study has filled a knowledge gap on the biological function and expression profiles of an essential digestive enzyme in sea cucumber, which may encourage future investigation toward rationalized diets for H. leucospilota in artificial cultivation, and optimized heterogenous prokaryotic systems for producing recombinant enzymes of marine origins.

Molecular cloning, expression and functional analysis of NF-kB1 p105 from sea cucumber Holothuria leucospilota

The nuclear factor-κB (NF-κB) family is evolutionary conserved and plays key roles in the regulation of numerous basic cellular processes. In this study, a sea cucumber Holothuria leucospilota NF-κB1 p105 named HLp105 was first obtained. The full-length cDNA of HLp105 is 6564 bp long, with a 219 bp 5′ untranslated region (UTR), a 2979 bp 3′ UTR, and a 3366 bp open reading frame (ORF) encoding for 1121 amino acids with a deduced molecular weight of 123.92 kDa and an estimated pI of 5.31. HLp105 protein contains the conserved domain RHD, IPT, ANK and DEATH. HLp105 mRNA can be detected in all tissues examined, with the highest level in the intestine, followed by the transverse vessel, rete mirabile, coelomocytes, respiratory tree, bolishiti, cuvierian tubules, body wall, oesophagus and muscle. Challenged by LPS or poly (I:C), the transcription level of HLp105 was apparently up-regulated in the tissues examined. Besides, Over-expression of HLp105 in HEK293T cells, the apoptosis was inhibited, and the cytokines IL-1β and TNF-α were activated. The results are important for better understanding the function of NF-κB1 p105 in sea cucumber and reveal its involvement in immunoreaction.

Modelling of aortic aneurysm and aortic dissection through 3D printing.

IntroductionThe aim of this study was to assess if the complex anatomy of aortic aneurysm and aortic dissection can be accurately reproduced from a contrast‐enhanced computed tomography (CT) scan into a three‐dimensional (3D) printed model.MethodsContrast‐enhanced cardiac CT scans from two patients were post‐processed and produced as 3D printed thoracic aorta models of aortic aneurysm and aortic dissection. The transverse diameter was measured at five anatomical landmarks for both models, compared across three stages: the original contrast‐enhanced CT images, the stereolithography (STL) format computerised model prepared for 3D printing and the contrast‐enhanced CT of the 3D printed model. For the model with aortic dissection, measurements of the true and false lumen were taken and compared at two points on the descending aorta.ResultsThree‐dimensional printed models were generated with strong and flexible plastic material with successful replication of anatomical details of aortic structures and pathologies. The mean difference in transverse vessel diameter between the contrast‐enhanced CT images before and after 3D printing was 1.0 and 1.2 mm, for the first and second models respectively (standard deviation: 1.0 mm and 0.9 mm). Additionally, for the second model, the mean luminal diameter difference between the 3D printed model and CT images was 0.5 mm.ConclusionEncouraging results were achieved with regards to reproducing 3D models depicting aortic aneurysm and aortic dissection. Variances in vessel diameter measurement outside a standard deviation of 1 mm tolerance indicate further work is required into the assessment and accuracy of 3D model reproduction.

Bunions, feet and battling nerve damage: is the sentinel vein a reliable landmark to locate the dorsomedial cutaneous nerve of the hallux?

Background Hallux valgus is a common condition in which the phalanges of the hallux deviate laterally and the first metatarsal deviates medially. The deformity is attributed to the long-term wear of tightly fitting footwear; however, a genetic predisposition may contribute to developing the condition. Surgical treatment of hallux valgus includes an osteotomy and rebalancing of the soft tissues. The sensory branch of the dorsomedial cutaneous nerve (DMCN) lies close to the surgical incision site and is at risk of iatrogenic damage. Sensory nerve damage following the procedure has been reported in up to 45% of patients. Objectives A previous study described a transverse vessel, named the sentinel vein, located immediately superficial to the DMCN. It was therefore suggested that the sentinel vein could act as a landmark for the DMCN. The objective of the current study was to recreate the work from this previous study as far as possible, and determine if the sentinel vein is a reliable landmark for the DMCN. Methods Cadaveric specimens were carefully dissected to observe both the appearance and position of the sentinel vein. Non-dimensional measurements were then taken to report the anatomical location of the vein. Results A preserved sentinel vein was observed in 18 out of 31 specimens. In all cases the DMCN was found to either lie immediately deep to the overlying sentinel vein or just distal at the point where the vein joined the plantar venous network. Subjectively, the appearance and position of the vein was seen to vary greatly between different specimens. Non-dimensional measurements placed the sentinel vein at a mean of 30.17% of the total metatarsal length. However intra- and inter-observer repeatability analysis of the results suggested that the measurements may not be reliable in accurately describing the location of the vein. Conclusion The variation in appearance of the sentinel vein between the specimens, along with the inability to reliably measure the position of the vein, indicates that the sentinel vein may not be a reliable landmark for the dorsomedial cutaneous nerve, and therefore the use of this structure as an anatomical landmark should be cautioned.

Microvascular alterations and the role of complement in dermatomyositis.

Different mechanisms have been proposed to explain the pathological basis of perifascicular muscle fibre atrophy in dermatomyositis. These include ischaemia due to immune-mediated microvascular injury, enhanced expression of type 1 interferon-induced gene transcripts in perifascicular capillaries and muscle fibres, and occlusion of larger perimysial blood vessels. Microvascular complement deposition is a feature of dermatomyositis pathology but the trigger for complement activation, the predominant complement pathway involved, or its role in the pathogenesis of the disease, has not been clearly defined. In the first step of this study we examined the density of capillaries and transverse vessels and searched for occlusion or depletion of larger perimysial blood vessels in 10 patients with dermatomyositis. This revealed an invariable association of perifascicular atrophy with capillary and transverse vessel depletion. The capillary and transverse vessel densities in non-atrophic fibre regions were not significantly different from those in muscle specimens of 10 age-matched controls. Next, in the same 10, as well as in 40 additional dermatomyositis patients, we searched for vascular deposits of IgG, IgM, and the C5b-9 complement membrane attack complex. Thirty-one of 50 dermatomyositis specimens contained C5b-9 reactive endomysial microvessels but none of these or other vessels reacted for IgG. Ten of 50 specimens harboured IgM-positive capillaries but only a few of these reacted for C5b-9. Finally, we analysed and compared different pathways of complement activation in dermatomyositis, lupus nephritis, and necrotic muscle fibres in Duchenne dystrophy. In lupus nephritis, C5-b9 deposits co-localized with IgG, IgM, C1q, and C4d, consistent with immune complex dependent activation of the classical complement pathway. In both dermatomyositis and Duchenne dystrophy, C5-b9 deposits co-localized with C1q and C4d and rarely with IgM indicating activation of the classical complement pathway. We conclude that: perifascicular atrophy in dermatomyositis is consistently associated with focal microvascular depletion, and that microvascular membrane attack complex deposits in dermatomyositis result from activation of the classical complement pathway triggered by direct binding of C1q to injured endothelial cells.

Pregnancy‐Induced Hypertension is Associated With Altered Anatomical Patterns of Hyrtl's Anastomosis

Umbilical arteries carry the blood from the fetus to the placenta and are typically connected by Hyrtl's anastomosis, a connection that is located near where the umbilical cord meets the placenta. The investigation of the anastomosis in pathological conditions, including pregnancy-induced hypertension is limited. Hence, 200 placenta and umbilical cords, 100 from normotensive and 100 from pregnancy-induced hypertensive subjects, were dissected and measurements were recorded. A single anastomosis between the umbilical arteries was observed in 167 specimens. In 16 cases, the two umbilical arteries were fused, in 15 cases there was no anastomosis, and in two cases there was a single umbilical artery. In one specimen from a normotensive case, a double anastomosis was observed. To our knowledge this is only the second report of this rare anatomical variant. When an anastomosis is present, the connecting vessel can be transverse to or form an oblique angle with the umbilical arteries. We observed a striking increase in the number of artery pairs connected by a transverse vessel in specimens from hypertensive subjects relative to those from normotensive subjects. Moreover, placentas from hypertensive donors were small if the umbilical arteries were connected by an oblique anastomosis. In addition, the length of the anastomosis and its distance from the cord insertion was shorter in specimens from hypertensive compared to normotensive subjects. We conclude that pregnancy-induced hypertension alters the anatomy of Hyrtl's anastomosis, and in some circumstances, the placenta.

Noninvasive Vascular Displacement Estimation for Relative Elastic Modulus Reconstruction in Transversal Imaging Planes

Atherosclerotic plaque rupture can initiate stroke or myocardial infarction. Lipid-rich plaques with thin fibrous caps have a higher risk to rupture than fibrotic plaques. Elastic moduli differ for lipid-rich and fibrous tissue and can be reconstructed using tissue displacements estimated from intravascular ultrasound radiofrequency (RF) data acquisitions. This study investigated if modulus reconstruction is possible for noninvasive RF acquisitions of vessels in transverse imaging planes using an iterative 2D cross-correlation based displacement estimation algorithm. Furthermore, since it is known that displacements can be improved by compounding of displacements estimated at various beam steering angles, we compared the performance of the modulus reconstruction with and without compounding. For the comparison, simulated and experimental RF data were generated of various vessel-mimicking phantoms. Reconstruction errors were less than 10%, which seems adequate for distinguishing lipid-rich from fibrous tissue. Compounding outperformed single-angle reconstruction: the interquartile range of the reconstructed moduli for the various homogeneous phantom layers was approximately two times smaller. Additionally, the estimated lateral displacements were a factor of 2–3 better matched to the displacements corresponding to the reconstructed modulus distribution. Thus, noninvasive elastic modulus reconstruction is possible for transverse vessel cross sections using this cross-correlation method and is more accurate with compounding.

Retrospective slice prescription compensation improves coronary cross-sectional area measurement by MRI

Background Measurements of coronary cross-sectional area are utilized in vasomotor tone and endothelial function studies, which typically employ breath-held, 2-D multi-slice imaging protocols wherein slices are prescribed orthogonally to a linear vessel segment (Fig 1a) [1],[2]. An ovoid template is then manually fitted to the transverse vessel images (Fig 1b) to measure cross-sectional area. Projection through the slice leads to dependencies between the measured area and the prescription angle (between the slice and the vessel–ideally 0°). This adds bias and reduces repeatability, which is problematic when detecting subtle dilations [3].

Real-Time Vessel Segmentation and Tracking for Ultrasound Imaging Applications

A method for vessel segmentation and tracking in ultrasound images using Kalman filters is presented. A modified Star-Kalman algorithm is used to determine vessel contours and ellipse parameters using an extended Kalman filter with an elliptical model. The parameters can be used to easily calculate the transverse vessel area which is of clinical use. A temporal Kalman filter is used for tracking the vessel center over several frames, using location measurements from a handheld sensorized ultrasound probe. The segmentation and tracking have been implemented in real-time and validated using simulated ultrasound data with known features and real data, for which expert segmentation was performed. Results indicate that mean errors between segmented contours and expert tracings are on the order of 1%-2% of the maximum feature dimension, and that the transverse cross-sectional vessel area as computed from estimated ellipse parameters a, b as determined by our algorithm is within 10% of that determined by experts. The location of the vessel center was tracked accurately for a range of speeds from 1.4 to 11.2 mm/s.

System for deep venous thrombosis detection using objective compression measures

A system for objective vessel compression assessment for deep venous thrombosis characterization using ultrasound image data and a sensorized ultrasound probe is presented. Two new objective measures calculated from applied force and transverse vessel area are also presented and used to describe vessel compressibility. A modified star-Kalman algorithm is used for feature detection in acquired ultrasound images, and objective measures of vessel compressibility are calculated from the detected features and acquired force and location data from the sensorized probe. A three-dimensional shape model of the examined vessel that includes compressibility measures mapped as colors to its surface is presented on the user interface, as well as a virtual representation of the image plane. The compressibility measures were validated using expert segmentation of healthy and diseased vessels and compared using paired t-tests, which showed a significant difference between healthy and diseased cases for both measures. 100% sensitivity and specificity were obtained for both measures. The system was implemented in real-time (16 Hz) and evaluated using a tissue phantom and on healthy human subjects. Sensitivity was 100% and 60%, while specificity was 97% for both measures when implemented. The initial results for the system and its components are promising.

Vein and artery growth after anastomosis with vascular closure staple clips vs interrupted polypropylene suture: application in pediatric vascular surgery

Background/Purpose Alternatives are still being sought in vascular surgery to address the problem of arrested growth after anastomosis in growing vessels, and opinions differ widely regarding the most suitable technique. This study compared vascular growth and permeability after anastomosis using the latest-generation vascular closure staple (VCS) system and the conventional suture technique to ascertain which approach yielded better results. Methods Thirty 55-day-old lambs underwent end-to-end anastomosis of the carotid artery and jugular vein. Serial ultrasonography and angiography were carried out over the ensuing 6-month growth period, after which lambs were euthanized. Results Both VCS clips and polypropylene suture allowed longitudinal and transverse vessel growth; however, longitudinal growth was significantly greater in clip-closed vessels than in either sutured or untreated vessels. Conclusions The results obtained for vascular growth and permeability suggest that VCS clips may provide a suitable alternative to conventional suture in pediatric vascular surgery.

Vascular Closure Stapler Clips Versus Polypropylene Sutures in End-to-End Anastomoses of Growing Arteries and Veins

Alternatives are still being sought in vascular surgery to avoid the complications caused in growing vessels by the various suture techniques and materials currently in use. A major complication is arrested growth following anastomosis. Opinions differ widely regarding the best approach to this problem, and research is currently underway at our center on the latest generation of clip appliers (vascular closure stapler, or VCS) and their potential application as an alternative to the conventional suture technique in pediatric vascular surgery. This study compared vascular growth and reendothelialization following anastomosis of growing arteries and veins using VCS clips versus the conventional interrupted polypropylene suture technique. Thirty 55-day-old lambs underwent end-to-end anastomosis of the carotid artery and jugular vein. Serial ultrasonography and angiography were carried out over the ensuing 6-month growth period, after which the lambs were euthanized. Gross examination of the anastomosis site was followed by histologic examination involving light microscopy, immunohistochemical techniques, and transmission electron microscopy. Although both VCS clips and polypropylene sutures allowed transverse vessel growth, the clips did not penetrate the intima and thus provided enhanced reendothelialization. The satisfactory results obtained here, as in earlier studies, increasingly point to VCS clips as the method of choice in pediatric vascular surgery.

Value of transesophageal echocardiography combined with computed tomography for assessing repaired type A aortic dissection

Thirty-two patients with repaired type A aortic dissection were examined by transthoracic echocardiography (TTE) (n = 32), transesophageal echocardiography (TEE) (n = 30), computed tomography (CT) (n = 29), or a combination of all 3, to assess course and complications as a function of the surgical procedure. The mean follow-up period was 55.7 months (range 3 to 132). Surgery consisted of a replacement of the ascending aorta in 25 patients (group 1) with extension to the transverse aorta in 7 (group 2). The transverse diameter of the aorta, the persistence of the false lumen, thrombus formation and flow dynamics in the false lumen were evaluated by TEE. Ten patients (31%) had a dilation in the initial ascending aorta (sinus of Valsalva aneurysm in 6 patients, and a false aneurysm in the other 4). Three of 4 patients with a proximal pseudoaneurysm underwent operation after TEE and CT evaluation. In the descending thoracic aorta, there was good agreement between TEE and CT scan determinations of transverse vessel diameter. Persistence of flow within the false lumen was significantly more frequent in patients with a dilated aorta (p < 0.05), whereas thrombosis was seen more often and false lumen less often in patients with nondilated aorta. No significant differences in vessel status or outcome were observed between the 2 groups, although this may have been due to the small size of group 2. TEE is thus a well-tolerated method for postoperative follow-up of type A aortic dissection whatever the type of surgery. For the upper ascending aorta, CT provided sufficient data.

Quantitative flow measurement of the carotid artery using a combination of intra-arterial digital subtraction angiography and ultrasound

Arterial blood flow was estimated using digital subtraction roentgen-densitometry in a model of the cervical arteries. The best results were obtained with two sampling windows calculating the mean passage time using the line of gravity of the contrast bolus. Mechanical contrast injection created a systematic error by acceleration. This procedure was then used for examining five patients. Quantitative blood flow measurements required knowledge of the transverse vessel area. This was determined by high resolution sonography. Blood flow was calculated as the product of cross-sectional area and mainstream velocity.

Exogenous Auxin andN-1 -Naphthylphthalamic Acid Effects onPopulus deltoidesXylogenesis

A method was developed for evaluating the empirical alteration of xylem vessel differentiation in the central leaf trace of Populus deltoides, a species that exhibits helical phyllotaxis. Effects of experimental treatments for a period of six plastochrons were evaluated by vessel parameter ratios = 2.PT/ (PT+1 + PT−1), where P was either vessel number or mean transverse vessel area measured at mid-intern ode at Leaf Plastochron Indices of T − 1, T, and T + 1. Excising leaf laminae reduced vessel number and mean vessel area in the associated central leaf trace by 50% and 70%, respectively, compared to unexcised laminae controls. Replacing excised laminae with a concentration series of exogenous indoleacetic acid (IAA) resulted in a 5% increase per log mol m−3 of IAA in the number of vessels differentiating in the associated central leaf traces compared to excised controls. Mean vessel areas within these leaf traces were 50% of those of intact leaf traces. No significant effects of different concentrations of exogenously applied IAA on mean vessel area could be demonstrated. A lanolin paste ring of N-1 -naphthylphthalamic acid (NPA), an auxin transport inhibitor, around the petioles of intact leaves reduced the number of differentiating vessels by 7% and mean vessel area by 29% per log mol m−3 of NPA compared to central leaf traces of leaves ringed with plain lanolin paste. The results suggest that NPA treatments may be used to distinguish experimentally, at least in part, the cell division from the cell enlargement phases of primary xylogenesis within central leaf traces of P. deltoides stems.

Theory and Experiment for the Effect of Vascular Microstructure on Surface Tissue Heat Transfer—Part II: Model Formulation and Solution

In this paper the conceptual three-layer representation of surface tissue heat transfer proposed in Weinbaum, Jiji and Lemons [1], is developed into a detailed quantitative model. This model takes into consideration the variation of the number density, size and flow velocity of the countercurrent arterio-venous vessels as a function of depth from the skin surface, the directionality of blood perfusion in the transverse vessel layer and the superficial shunting of blood to the cutaneous layer. A closed form analytic solution for the boundary value problem coupling the three layers is obtained. This solution is in terms of numerically evaluated integrals describing the detailed vascular geometry, a capillary bleed-off distribution function and parameters describing the shunting of blood to the cutaneous layer. Representative heat transfer results for typical physiological conditions are presented.

STUDIES ON THE TAPEWORM ANOPLOCEPHALA PERFOLIATA (GOEZE, 1782).

1. The exrectory system of Anoplocephala perfoliata has been re-described and shown to consist of a dorsal ‘network’ system of vessels to which the flame cells are connected and a ventral pair of longitudinal vessels linked only by a transverse vessel in each proglottid.2. The two excretory systems unite only in the apical ramifying vessels of the scolex.3. Alkaline phosphatase activity was demonstrated in the cuticular microvilli, the subcuticular region and in the excretory vessels.4. Non-specific esterase, insensitive to 10−4m E 600, was located in the lappets and embryonated eggs and esterases, inhibited by 10−4m E600, in parts of the cuticle and subcuticular region and parenchyma.5. Cholinesterases were found in the nervous system and in the reproductive ducts.6. Aminopeptidase was found in the neck region, in the undifferentiated proglottids, the active testes and ovaries, the male reproductive ducts and in the region of high metabolic activity in the fringe of the proglottid.

The Blood-system in the Serpulimorpha (Annelida, Polychaeta) : 1. The Anatomy of the Blood-system in the Serpulidae

ABSTRACT 1. An account will be given of the anatomy of the blood-system of Pomatoceros triqueter, and of comparative observations on the following serpulids: Serpula vermi- cularis, S. lo-biancoi, Hydroides norvegica, Vermiliopsis infundibulum, Salmacina incrustans, Protula intestinum, P. tubularia, Apomatus ampulliferus, A. similis, Spirorbis militaris, and S. corrugatus. 2. In all species there is a central blood-system of large vessels in which blood circulates in the usual manner, and a peripheral system of small blind-ending vessels which are alternately full and empty, receiving their blood from the central system, then returning it along the same channels to the central system. 3. The central blood-system is as follows: Blood moves from the tip of the abdomen to the front of the thorax through a sinus enveloping the alimentary canal. Anteriorly it passes through dorsal, transverse, and circum-oesophageal vessels to a ventral vessel in which it moves backwards to the tip of the abdomen. A pair of ring vessels connects the ventral vessel with the sinus at the posterior end of each segment. 4. The anterior end of the dorsal vessel in Pomatoceros triqueter, Serpula vermi- cularis, Hydroides norvegica, and Vermiliopsis infundibulum is surrounded by a sphincter muscle of unknown function, and contains a muscular valve which probably obstructs the back-flow of blood from the transverse vessel. Protula intestinum possesses the valve but lacks the sphincter. Salmacina incrustans and Spirorbis militaris have neither valve nor sphincter. 5. The peripheral blood-system has the following components: the branchial vessels with branches in the crown; the vessels of the collar and lips; the peri-oesophageal plexuses; the trans-septal vessels supplying the body-wall, parapodia, and thoracic membrane. 6. In Pomatoceros triqueter the opercular vessel is spirally coiled, but in other serpulids it is characteristically branched. 7. When Pomatoceros withdraws into its tube, movement of blood in the crown ceases. The operculum is therefore not used as a special respiratory organ when the crown is retracted. 8. The oesophagus of Pomatoceros is surrounded by two independent blind-ending vascular plexuses, an outer plexus communicating with the gut sinus and an inner plexus with the circum-oesophageal vessels. Serpula vermicularis is probably the same. Hydroides norvegica and Protula intestinum lack the outer plexus. Salmacina and Spirorbis have neither plexus. 9. The body-wall of each segment derives its blood-supply from trans-septal branches of the ring vessels of the preceding segment. In Salmacina and Spirorbis these trans-septal vessels are unbranched. In larger serpulids they have numerous [Quarterly Journal of Microscopical Science, Vol. 91, part 2, June 1950.] branches under the epidermis, in the parapodia, and in some cases on the coelomic surface of the body-wall. Branches of the thoracic trans-septal vessels supply the thoracic membrane. In all species except Salmacina, Spirorbis, and Protula intestinum the thoracic trans-septal vessels end ventrally in two superficial ventro-lateral longitudinal vessels which communicate either with the circum-oesophageal vessels or with the ventral vessel. In P. intestinum the thoracic trans-septal vessels enter the ventral vessel directly. The pattern of superficial vessels on the ventral surface of the thorax is useful for identifying specimens. 10. Lateral vessels, such as are found in Sabella, are absent in all serpulids.