Centripetal End Research Articles

Comparative morphology of the carpel in the Liliaceae: Veratreae

The genera of the Veratreae, a tribe of the Melanthioideae, have many features in common: there are usually many ovules, except for Amianthium (with 2 4), arranged in 2 -4 longitudinal placental rows per carpel; all are bitegmic, basipetal, and campylotropous. Of 37 species examined, only 2 have open sutures at the lowermost level of ovular insertion, but 13 species have holes in the centre of the pistil. These holes may represent possible stages in the evolutionary closure of previously open sutures. Most flowers were epigynous, only 11 being hypogynous-perigynous. The tribe as a whole is marked by the presence of 3 composite (heterologous) vascular bundles, composed of joined staminal and tepallary bundles alone and 3 composite bundles, as above, fused to a dorsal bundle. The bundles were united below the locular base in all genera except Schoenocaulon and Toxicoscordion. Two major kinds of central cylinder arrangement occurred at the level of the lowermost ovular insertion: either 6 inverted ventral bundles or 6 simple septal bundles, with normally arranged (or sometimes inverted) xylem and phloem centrifugally located and 6 simple placental bundles, with inverted xylem and phloem, at the centripetal end of the septum. Generally each septal bundle united with its nearest adjoining placental bundle about the mid-locular level.

Rhizoid Differentiation in Spirogyra

Localization of phytochrome which mediates rhizoid differentiation in Spirogyra was investigated. The red-absorbing form of phytochrome (Pr) seems to be distributed all over the cell periphery which remained in the centripetal end part after the centrifugation, as rhizoids formed equally well with red spotlight irradiation of three different parts of an end cell, i.e. distal end, middle, and proximal end, and with irradiation of centrifugal and centripetal end parts of a centrifuged end cell. The Pr distribution was confirmed with an experiment using far red irradiation over the entire cell, centrifugation, and red spotlight irradiation. The Pr-phytochrome molecules appeared to be mobile because no dichroic orientation was shown with polarized red spotlight irradiation. On the contrary, it is suggested that far red-absorbing form of phytochrome molecules are evacuated from the centripetal end part by the centrifugation in an experiment involving red irradiation over the entire cell-centrifugation-far red spot irradiation. Rhizoid formation was repressed markedly by far red irradiation of the centrifugal end part but not of the centripetal end part.

Physical properties of blue-green algae: Ultracentrifugation and electron microscope studies

The Feulgen-positive and envelope-free nucleoplasm ofAnabaena andGloeocapsa contains DNA filaments. When ultracentrifuged it is displaced between the maze of photosynthetic lamellae to form a continuous, flattened layer in the centripetal half of the cell. The absence of a mesosome and lack of attachment of the nucleoplasm to the plasmalemma make the method of duplication and separation of the genome to the progeny an enigma. In the centripetal end of ultracentrifugedAnabaena, the photosynthetic lamellae are somewhat stretched and sometimes broken. This condition suggests that the cortical positioned photosynthetic lamellae are tightly connected in several places along their surfaces to an undisplaced cortical cytoplasmic layer. It is uncertain whether or not they are also directly attached to the plasmalemma. A vesicle is often observed in the centripetal end of the cell; it probably represents for the most part, the contents of distorted intralamellar spaces. In ultracentrifugedGloeocapsa, the photosynthetic lamellae show little displacement. They appear attached, probably at their ends to the plasmalemma and, likeAnabaena andNostoc, they possess phycobilisomes which are not greatly affected by ultracentrifugation. Cells usually survive a centrifugal force greater than required to separate most nonliving protein systems. When subcultured, a redistribution of the displaced components usually occurs and growth is resumed.

Progesterone-induced in vitro maturation in oocytes of Notophthalmus viridescens (Amphibia Urodela) and some observations on cytological aspects of maturation

Maturation in vitro of oocytes of the newt, Notophthalmus viridescens, is inducible with progesterone after in vivo treatment of females with gonadotropin; few oocytes mature in vitro in the absence of such gonadotropin treatment. Chromosomes of most large oocytes of animals not receiving gonadotropin are still in the lampbrush condition; chromosomes from gonadotropin-treated animals are shorter and the lateral loops are less profuse and somewhat retracted. The chromosome condition, then, can be correlated with susceptibility to progesterone induction of maturation in vitro. As maturation progresses, the germinal vesicle moves toward the surface and decreases in size, with an apparent loss of nuclear material from the centripetal end. Although lateral loops of most chromosomes disappear during the changes in the germinal vesicle, profuse loops develop during this period at the sphere loci, which were previously devoid of loops.

A cytological study of the centrifuged whole, half, and quarter eggs of the sea urchin, Arbacia punctulata.

While the ooplasmic components of centrifuged eggs of Arbacia punctulata do not stratify in homogeneous layers, we have obtained the following strata beginning with the centripetal end: lipid droplets, pronucleus, clear zone, mitochondria, yolk, and pigment. Whereas mitochondria may be found mingled with yolk bodies, we have never observed lipid droplets nor pigment bodies among any of the other inclusions. The so-called clear zone contains a heterogeneous population of inclusions: annulate lamellae, heavy bodies, Golgi complexes, and rod-containing vacuoles. The peripheral cortical granules of immature (germinal vesicle stage) and of mature eggs are not dislodged from the cortical ooplasm with the centrifugal force utilized. When the eggs are treated with urethane, prior to centrifugation, the cortical granules of mature eggs abandon their peripheral position. Further centrifugation of the initially stratified eggs produces nucleated and nonnucleated halves and the centrifugation of the halves results in quarters. The cytology of the halves and quarters is discussed. The halves and quarters have been activated with either sperm or hypertonic sea water. With the exception of the nucleated halves, we were unable to obtain plutei larvae from the other fractions (red halves and quarters). We believe that the lack of development of the various fragments is a function of the balance of particular inclusions necessary for differentiation.

Electron microscope and ultracentrifugation studies on the rat reticulocyte.

AbstractReticulocytosis was induced in rats by the daily injections of phenylhydrazine. The reticulocytes were studied by supravital staining, ultracentrifugation and phase‐contrast and electron microscopy. Electron micrographs of sectioned reticulocytes reveal the presence of hemoglobin, polyribosomes, mitochondria, micropinocytosis vesicles, tubules of varying size and, in some cases, Heinz body material. When subjected to ultracentrifugation these materials are readily stratified in the order of their relative densities from the centrifugal to the centripetal end as follows: hemoglobin, mitochondria, ribonucleoprotein material (ribosomes) and Heinz body material. The centrifuged reticulocytes may be stretched two or three times their normal diameter and even pulled into two parts without hemolysis. Of interest is the observation that in ultracentrifuged reticulocytes, the ribosomes are not displaced from the region of the cortex, a condition which is interpreted as strong evidence that this region is of a greater consistency (viscosity) than the remainder of the cell. Evidence was observed to show that as maturation of the reticulocyte occurs, the cell gradually decreases in size and increases in density; concomitantly with these changes is a progressive degradation of the mitochondria and ribonucleoprotein material, so that by the time the erythrocyte stage is reached, these materials seem to have completely disappeared.

フークス科藻類の発生力学XVII.

Eggs of Coccophora Langsdorfii was ultracentrifuged just after fertilization at 25, 000 times gravity for five minutes. As a result, the following was discovered.(1) The intracellular materials are stratified into at least five layers. Arranged in order from the centripetal end, they are: the oil cap, the transparent layer of free water, the plastids and nucleus layer, the hyaline cytoplasm layer, and the granules layer.(2) When the centrifuged egg is immersed in distilled water, or in hypotonic sea water below 30per cent in concentration, the granules stratified in the centrifugal zone are darkened in color and the darkening begins at or near the centrifugal end and then spreads towards the centripetal side, then the plasmoptysis occurs in the centrifugal half. This indicates that the water permeability is highest at the centrifugal end.(3) When the centrifuged egg is immersed in the solution of the starfish toxin at or over 10-4 in concentration, the plasma membrane is destroyed in the subcentripetal zone surrounding the layer of hyaline cytoplasm. This indicates that a certain differentiation in susceptibility to starfish toxin has taken place in the plasma membrane or the cortical layer with the centrifugation. That is, the cortical layer including the plasma membrane is also movable by centrifuging, though the movement is invalid in determining the polarity axis.

フークス科藻類の発生力学XVIII.

Young embryos of Coccophora Langsdorfii just differentiating the primary rhizoids were ultracentrifuged at 25, 000 times gravity for five minutes. As a result, the following was discovered.(1) The cell of normal young rhizoid contains plastids, the nucleus, pale globules and the cytoplasm matrix. The plastids are localized in the distal region, the nucleus in the middle, and the pale globules in the proximal region. When the rhizoid is centrifuged laterally, each of these elements is stratified centripetally in each zone. This indicates that their specific gravities are smaller than that of the hyaline matrix of cytoplasm.(2) If the rhizoid is centrifuged in the proximal or in the distal direction, the pale globules are also stratified to the centripetal end, while the plastids and the nucleus are gathered to the centrifugal being separated from the pale globules by a transparent zone intervening.(3) The pale globules are considered to be a kind of physodes, having properties reducing ferric ions and Fehling's solution.

Studies on the fine structure of ultracentrifuged spinal ganglion cells.

THE FOLLOWING STRUCTURES WERE OBSERVED IN ELECTRON MICROGRAPHS OF THE MOUSE SPINAL GANGLION CELLS: Nissl bodies composed of both aggregated rough-type, largely oriented, membranes of the endoplasmic reticulum and discrete particles; short rodlike mitochondria with well-developed transverse, obliquely or longitudinally arranged cristae, and a relatively typical Golgi complex. The components of ultracentrifuged ganglion cells (400,000 times gravity for 20 minutes) are stratified, the layers appearing in the order of their decreasing density as follows: (1) A microsomal or ergastoplasmic layer which may be further divided into three sublayers without sharp boundaries, namely, a discrete particle layer, a layer of discrete particles and highly distorted membranes of the endoplasmic reticulum, and a layer composed of relatively intact, but stretched membranes of the endoplasmic reticulum and discrete particles. (2) Mitochondria constitute a relatively broad layer. They are sometimes stretched; however, they retain most of their fine structure. The stratified nucleus is found within the mitochondrial layer. (3) A relatively wide layer of tightly packed vesicles. (4) At the centripetal end, resting against the cell membrane, are a few lipid vacuoles. A comparison is made between the ultrastructure of the stratified layers in situ and those described by others in differentially ultracentrifuged homogenates.

Cytochemistry of centrifuged hyphae of Neurospora

Living hyphae of Neurospora crassa were centrifuged at 50,000 × g where-upon their contents sedimented into the following layers (starting at the centrifugal end): glycogen, ergastoplasm, mitochondria, nuclei, “supernatant” enchylema, vacuoles, and fat. Hyphae survived centrifugation and were able to grow again after the stratified cell organelles became redistributed in the cell. Cytochemical tests were performed on centrifuged mycelia, either living or fixed by freeze-substitution or by formol. Schematic figures summarize the results. Pauly's reaction for proteins was strongest in the mitochondria, while Sakaguchi's reaction was strongest in the ergastoplasm. Protein-bound SH groups were highest in the ergastoplasm and the nucleoli. Ribonucleic acid was highest in the ergastoplasm, low in the mitochondria and nuclei, and not detectable in the enchylema. Deoxyribonucleic acid was restricted to the nuclei. Glycogen was in a clearly limited centrifugal layer while other carbohydrates (Hotchkiss test) were found in the ergastoplasmic layer as well. Fat (Sudan IV) was at the centripetal end; osmiophilic material was found below the fat layer and in the mitochondria and the nucleoli. The vacuoles contained metachromatic granules. The following enzymes were restricted to the mitochondria: succinic dehydrogenase, cytochrome oxidase, peroxidase, β-galactosidase, and acid phosphatase (Rutenburg and Seligman test). Alkaline phosphatase was found in the enchylema and the nucleoli, and a weak acid phosphatase (Gomori test) in the enchylema. The advantages of using living centrifuged cells as opposed to centrifuged homogenized material for a study of the biochemistry of cell organelles are discussed in detail. While the results of both methods were found to be in general agreement, some products of homogenization were considered to represent artifacts. The separation of cell organelles by centrifugation provides also a useful tool for the study of the intracellular resolution of different cytochemical methods.

Developmental mechanics of fucaceous algae XII. Further studies on the blister formation in fucoid eggs

(1) Blister formation occurs when eggs ofCoccophora Langsdorfii, Fucus evanescens, andSargassum confusum are immersed in zinc chloride solution at a density higher than 25 per cent. (2) When the egg is stained vitally with brilliant green, neutral red, or with toluidin blue, then immersed in zinc chloride, coloured blisters appear, and their colour is the same as that of the stained egg. (3) A giant oily blister appears at the centripetal end where the oil drops were stratified but normal blisters appear in the other region, when the centrifuged eggs are immersed in zinc chloride. (4) Normally, the blister, seems to be the extrusion of the hyaline plasm through small holes of the plasma membrane made by zinc chloride.

クロマツの卵細胞内に存在する蛋白胞の細胞化学的研究

1. The “proteid vacuoles” in the cytoplasm of egg cell of Pinus thunbergii were studied with staining methods.2. The proteid vacuoles first appear in the central cell. With maturation of the egg cell, they increase more and more in number and in their stainability by Heidenhain's iron-hematoxylin and protein-staining reactions. The number and the stainability of them reach the maximum state just before fertilization. After fertilization they begin to decrease in number and nearly completely disappear by the time of proembryo formation at the base of the egg cell.3. The proteid vacuoles contain not only protein but also PNA and a little polysaccharides.4. In all the stages of oogenesis, the proteid vacuoles are separated into three groups by centrifuge treatment; the first of them are moved toward the centrifugal end, the second toward the centripetal end and the remaining ones are distributed in the middle part of the cell. Those gathered at the centripetal end under centrifugal force are propable to contain lipids.5. The nutritive significance of the proteid vacuoles in the maturation of egg cell and in the early development of proembryo is discussed.

Phase-Contrast and Electron Microscope Studies on the Golgi Bodies and Mitochondria of the Germ Cells of <i>Helix aspersa</i>

1. The Golgi bodies of the male germ cells of Helix aspersa have been observed in the living cells by aid of the phase-contrast microscope. Their form and distribution are exactly like those seen in fixed material. Accordingly, they cannot be artifacts induced by the methods used to demonstrate them.2. In electron micrographs the Golgi bodies have the same form and distribution as those seen in the living cell under the phase-contrast microscope. In addition, they (osmiophilic portion of fixed and impregnated material) are relatively opaque to the electrons, yet display a fine fibrous internal structure. On the inner side, i.e., that of the lesser curvature of the crescent and ring-like Golgi bodies, is seen a highly vacuolated region which probably corresponds to the osmiophobic region of the classical description. However, here this vacuolated region does not seem to be a morphological part of the Golgi bodies, but appears more like a region of active synthesis probably associated with the function of the Golgi material.3. In ultracentrifuged cells the mitochondria are displaced to the centrifugal end and the Golgi bodies to the centripetal end of the cell. This demonstrates that the Golgi bodies differ sharply in relative specific gravity from the mitochondria.4. Mitochondria in electron micrographs were observed composed of longitudinal striations which may in reality, be lamellae. Mitochondria are distinct from the Golgi bodies.

Memoirs: A Cytological Study of the Centrifuged Oocyte of the Mouse

1. The ovaries of the mouse were ultra-centrifuged at a force of about 130,000 times gravity. 2. The young oocyte is stratified into three layers: lightly stained cytoplasm, usually containing a few small granular Golgi elements, in the centripetal end of the cell; a middle layer of Golgi elements containing the nucleus; a centrifugal layer of mitochondria. 3. In the larger oocytes a thin layer of yolk is present between the Golgi layer and the centripetal pole, while a layer of nongranular substance is present at the centrifugal pole. 4. The mature oocyte is stratified into four layers: a lightly stained centripetal layer; a layer of yolk; the Golgi layer; a centrifugal layer of mitochondria. The Golgi layer is now divided into two parts; the centrifugal part contains numerous mitochondria amongst the Golgi elements. 5. The nucleolar material is the heaviest substance in the nucleus; it increases in density with the growth of the egg. In the mature oocyte the nucleus lies in the mitochondrial layer; the nucleus is thrown towards the centrifugal pole by the weight of the nucleolus. 6. The Golgi elements are in the form of granules, rods, and of irregularly shaped bodies. It is probable that the localized Golgi material of the mouse egg is not in the form of a network. 7. Fat was not identified in the normal ovarian eggs, but is present in degenerating ova. The Golgi elements give rise to the fat of degenerating eggs. 8. The inclusions and components of the follicle-cells were not always affected by the force necessary to bring about stratification of the oocyte. The degenerating eggs were not stratified.

Effect of Ultra-centrifuging the Oocytes of the Mouse

OVARIES of the mouse were centrifuged in the Beams ultra-centrifuge. In the young oocytes the cytoplasmic inclusions and components are stratified into three layers. The mitochondria occupy the centrifugal end of the cell. The Golgi material and the nucleus, together with a few small granular mitochondria, are situated in the middle region of the cell, while the centripetal end is filled with clear cytoplasm which may contain a few small Golgi elements.

A cytological study of the Gregarine Parasites of Tenebrio molitor, using the Ultra-centrifuge

ABSTRACT A. Three gregarine species are found to inhabit the mid-gut of the mealworm larvae used: Gregarina cuneata Stein, Gregarina polymorpha Hamm, and Gregarina steini Berndt. The often described Steinina ovalis is probably seldom or never found. They live only in the mid-gut of larvae. They are never found in pupal or adult forms. Gregarines have been seen moving when in a stratified condition. B. The gregarine cytoplasm has five important inclusions, each having a characteristic position in a centrifuged animal (Text-fig. 2). Paraglycogen.—This gives a dark brown colour with iodine, a pinkish general colour with the acid fuchsin of the Feulgen technique, and often a red colour with Bauer’s reaction. It occupies the centrifugal pole of the centrifuged cell and is in the form of disc-like granules of varying size. In young centrifuged Gregarina steini chromidial granules are seen in the paraglycogen area, and have, therefore, approximately the same specific gravity. They arise by karyosomic budding with the subsequent extrusion of these buds into the cytoplasm. They stain with iron alum haematoxylin, like the karyosome, and both give a negative result with the Feulgen test for thymonucleic acid. They probably correspond to Joyet-Lavergne’s ‘albuminoid reserves’, but do not have the mitochondrial ‘cap’ he describes. Mitochondria.—These are usually granular, but sometimes rod-like. They are seen between the ‘alveoli’ formed by the paraglycogen granules. They lie distally to the paraglycogen in a centrifuged parasite ; they stain by the iron alum haematoxylin long method, after Benoit, Champy, or Altmann fixation, also with Altmann’s fuchsin picric acid stain and the Bensley Cowdry modification of it. The Nucleus is karyosomic, and the karyosome is moved to the centrifugal pole by pressure as is the nucleolus of metazoan cells. The nucleus shows budding of the karyosome. There is plasmatic as well as chromatic material in the karyosome, as shown by centrifuging. The nucleus gives a negative result with Feulgen’s nuclear reaction, but chromatin may exist in a very dispersed condition. Golgi Material.—This lies at the centripetal end of the nucleus. It is hest shown by Weigl fixation. The large and regular Golgi elements are slightly heavier than the granular Golgi material, which may be compared with that of young oocytes. Fatty Material lies at the extreme centripetal pole of the cell, in globules of varying size. It becomes brown or black after treatment with osmium tetroxide, and vivid cherry red with Sudan IV. It gives a negative result with the Schultz reaction for cholestrol. C. Large globules are seen in the protomerite of Gregarina steini, eosinophile, sometimes fuchsinophile, and also staining with methylene blue. These move towards the centrifugal pole. Methylene blue preparations show blue granules among the paraglycogen granules in the centrifuged animal. They are remarkably resistant to dilute sulphuric acid. They are possibly allied to volutin or chromidia. Tests for the presence of Vitamin C yielded negative results. Only the inclusions of the gregarines in the gut lumen were studied, and the complete life-cycles of the species were not followed out.

Segregation of "Cleavage-Substance" in the Unfertilized Egg of Dendraster excentricus.

The unfertilized eggs of the sand-dollar, Dendraster, which normally are shed from the ovaries fully mature, were sedimented by centrifuging at approximately 40,000 gravities for 7-10 minutes, with the result that the eggs were elongated to dumb-bell-shape and pear-shape and the nucleus thrown to the extreme centripetal end, against the “oil-cap”. The eggs were then caused to develop parthenogenetically by means of a modified Loeb's method of acidulated sea water and hypertonic treatment. With respect to the effects of sedimentation on subsequent development, the eggs of different individuals behaved somewhat differently. On the basis of types of cleavage the females whose eggs were used may be classed in three groups, namely, (1) those whose eggs show complete but unequal segmentation, cleavage of the centripetal (nucleated) end being retarded so that as a result the blastomeres are abnormally large there, rapid cleavage at the centrifugal end resulting in blastomeres of approximately normal size; (2) th...

Effect of Digitalis Administration on Experimental Hypertrophy.

In preliminary experiments it was observed that, after fertilization, the eggs of Strongylocentrotus purpuratus showed, near the periphery, light and dark phases when rotated between crossed Nicols. The effect, however, was partially masked by the opaque granules of the cytoplasm. In order to eliminate this difficulty the unfertilized ova were centrifuged at approximately 60,000 gravities for 3 minutes, flotation of the eggs being insured by the addition of sufficient M/l solution of sucrose to the sea water in the tubes. After centrifugation the eggs were transferred to sea water and microscopic preparations made in the usual way. The eggs appeared elliptical in shape, with the nucleus at the centripetal end and the opaque granules at the opposite pole occupying about ⅓ of the egg. The remaining ⅔ of the egg was transparent and showed no bire-fringent effects with polarized light. Within 3 minutes after fertilization, however, when the membrane was forming and afterward, the clear cytoplasm gave evidence of birefringence so definite that the angle between light and dark phases could be measured. In all 35 measurements of the angle were made and these yield a mean value of 31°, with extremes of 24° and 37°, the intermediate values being consistently distributed on a probability curve. Now the optical section of the egg is something less than 72μ, and since such a minute quantity of polarizing molecules (e. g., sugar) in solution would not be sufficient to rotate the beam of polarized light, it is necessary to assume that the rotation is due to a regular grouping of molecules to form a multimolecular lattice with birefringent properties similar to those of a crystal, a starch grain, a filament of silk, a muscle fibril.

Occurrence of Birefringence in the Fertilized Egg of the Sea Urchin

In peiiminary experiments it was observed that, after fertilization, the eggs of Strongylocetrotus purpuratus showed, near the periphery, light and dark phases when rotated between crossed Nicois. The effect, however, was partially masked by the opaque granules of the cytoplasm. In order to eliminate this difficulty the unfertilized ova were centrifuged at approximately 60,000 gravities for 3 minutes, flotation of the eggs being insured by the addition of sufficient M/1 solution of sucrose to the sea water in the tubes. After centrifugation the eggs were transferred to sea water and nlicroscopic preparations made in the usual way. The eggs appeared elliptical in shape, with the nucleus at the centripetal end and the opaque granules at the opposite pole occupying about ⅓ of the egg. The remaining ⅔ of the egg was transparent and showed no birefringent effects with polarized light. Within 3 minutes after fertilization, however, when the membrane was forining and afterward, the clear cytoplasm gave evidence of birefringence so definite that the angle between light and dark phases could be measured. In all 35 measurements of the angle were made and these yield a mean value of 31°, with extremes of 24° and 37°, the intermediate values being coilsistently distributed on a probability curve. Now the optical section of the egg is something less than 72μ, and since such a minute quantity of polarizing molecules (e. g., sugar) in solution would not be sufficient to rotate the beam of polarized light, it is necessary to assume that the rotation is due to a regular grouping of molecules to form a multimolecular lattice with birefringent properties similar to those of a crystal, a starch grain, a filament of silk, a muscle fihril.

The effect of ultracentrifuging on Paramecium, with special reference to recovery and macronuclear reorganization

AbstractParamecium caudatum becomes much elongated upon centrifuging at 21,000 times gravity. The chromatin is sometimes forced from the achromatic matrix of the macronucleus. The materials in the cell are redistributed according to their relative specific gravities as follows: At the centrifugal end of the cell, crystals, layer of fluid, micronucleus and macronuclear chromatin, food vacuoles and neutral red inclusions, achromatic matrix of the macronucleus, endoplasm with large clear alveoli, and fat, at the centripetal end of the cell. The contracting vacuole is displaced sometimes but not the feeding canals or pore. In some cases the crystals, micronucleus and macronuclear chromatin may be extruded from the cell. Animals which survive centrifuging regain their usual shape and the disturbed materials return to their usual distribution rapidly. Sometimes the crystals remain in large compact masses and are so passed to the daughter cells upon fission. The two components of the macronucleus do not fuse the macronuclear chromatin regenerates an achromatic matrix, and division is somewhat delayed. The old macronuclear matrix persists over a long time and sometimes interferes with division. Animals which have no micronucleus may survive and divide, but no amicronucleate races have been established. Apparently macronuclear chromatin is necessary for the survival and division of P. caudatum; in the absence of the macronuclear chromatin no replacement occurs from the micronucleus. The membrane of the contracting vacuole is temporary.