摘要:

AbstractThe mitotic index\documentclass{article}\pagestyle{empty}\begin{document}$ \left({\frac{{{\rm number\,of\,dividing\,cells}}}{{{\rm total\,number\,of\,cells}}}} \right) $\end{document}of the neural crest and its derivativesin situwas determined in serially‐sectioned embryos of the black (DD or Dd) and white (dd) strains of the Mexican axolotl,Ambystoma mexicanum,Shaw, to see whether the differences between the strains in the number and distribution of their initial complement of melanophores could be causally related to differences in the pattern of development of their respective neural crests.Prior to and during the initial appearance of melanophores, the mitotic index of the neural crestin situin the black axolotl is significantly greater than in the white. Concommitantly, there are more crest cells in the black than in the white prior to crest cell migration. However, during the periods of maximum crest cell migration and initial appearance of melanophores, there are significantly more crest cellsin situin the white than in the black. These crest cellsin situin the white are clumped together mid‐dorsal to the neural tube, while in the black they show the dispersion typical of migrating crest cells.Following the initial appearance of melanophores, there are no differences between the strains in the number of melanophores dorsal to the neural tube and somites, but there are significantly more crest‐derived cells in this area in the black than in the white. The latter difference between the strains may be causally related to the significantly greater number of cells in the early spinal ganglia of the black axolotl than in the

ISSN:0022-104X    

DOI:10.1002/jez.1401790302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractBovine prolactin stimulates growth of tadpoles, whereas bovine growth hormone stimulates growth of postmetamorphic frogs. The biochemical composition of liver, muscle, and fat body were examined to determine whether there were any changes in carbohydrate, protein, fat, or nucleic acids which might correlate significantly with the growth effects of the hormones in the two stages of development. In the frog, the major effect of growth hormone was to depress carbohydrate and lipid stores, with little or no effect on protein and nucleic acids in most experiments. Prolactin had similar but smaller effects on carbohydrate, and no effect on fat body lipid in the frog. In tadpoles prolactin suppressed muscle glycogen, but otherwise did not affect tissue composition. Growth hormone had no effects in the tadpole. Ways in which the interrelated developmental and metabolic effects of growth hormone and prolactin could increase the adaptive significance of distinct larval and postmetamorphic growth‐regulating hormones in the amphibians are discusse

ISSN:0022-104X    

DOI:10.1002/jez.1401790303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractThe mechanism of puparium formation in the fleshflySarcophaga bullataParker was studied. Several distinct morphological events take place during the hour prior to the completion of the white puparium. 1. The anterior three larval segments are irreversibly retracted. 2. The body contracts by muscular action to about two‐thirds of its original length. 3. Simultaneously a longitudinal shrinkage occurs in the cuticle, giving it a smooth surface. 4. Finally the cuticle becomes stabilized in the sense that it can no longer be stretched, and no longer collapses upon release of internal pressure by bleeding. 5. Tanning starts almost as soon as the smooth barrel shape of the puparium is completed. The following observations demonstrate the largely independent nature of these processes: 1. Paralyzing the musculature, by ligation, tetrodotoxin, or bee venom, leads to tanned puparia in the shape of the larva. 2. Disabling the shrinkage system (e.g., by ryanodine or eserine) leads to puparia with a deeply folded surface. 3. Injecting smaller doses of tetrodotoxin or bee venom leads to elongated puparia with a shrunken (smooth) surface. 4. Injecting a certain ecdysone analogue leads to a puparium which is normal except for the failure of the anterior end to retract. 5. Release of internal pressure by bleeding leads to puparia which are supercontracted and folded. 6. Injection of a tanning inhibitor (α‐MDH) leads to a white puparium of normal shape which fails to tan. The transformation of the larval cuticle into the tanned puparium is accompanied by a spectacular water loss in the cuticle which is particularly rapid during the brief period between completion of the white puparium and start of tanning. This water loss is almost certainly correlated with the above mentioned stabilization of the pupa

ISSN:0022-104X    

DOI:10.1002/jez.1401790304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractThe chemical composition of cartilage from vertebrae and long bones of chick embryos 8 to 18 days old has been established. Collagen, muco‐polysaccharides, and non‐collagenous protein show similar patterns of distribution in the two types of cartilage; the maximum variation in these components has been found between the fourteenth and the sixteenth day of the prehatching period. The modifications that we have measured seem to be related more to a general biochemical feature of embryo development than to the preparation of the cartilage matrix for calcificat

ISSN:0022-104X    

DOI:10.1002/jez.1401790305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractThyroidectomy of Starlings prior to exposure to long photo‐periods (17L:7D) resulted in a failure of testes to regress after an initial size increase. Thyroidectomy after four weeks of such exposure resulted in testicular regression followed by a second period of size increase. Testicular size was correlated with androgen secretion as indicated by yellowing of the bill. The effect of thyroidectomy was not due to increased gonadal sensitivity to gonadotrophins and not due to the requirement of the presence of the thyroid for regressionper se. Presumably thyroidectomy results in higher gonadotrophin secretion.Thyroidectomy did not affect the termination of the photorefractory period in the fall.Thyroidectomized Starlings had higher body weights than control

ISSN:0022-104X    

DOI:10.1002/jez.1401790306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractLanthanum, a tracer of extracellular space in fixed tissue, readily traverses the follicular epithelium of the lizardAnolis carolinensis. Saccharated iron oxide injected into living lizards and peroxidase administeredin vitropass through the extracellular spaces of the follicular epithelium and accumulate in the zona pellucida. Micropinocytotic uptake of iron and peroxidase by the oocyte occurs in larger follicles which show signs of yolk accumulation. These findings confirm the morphological absence of sealing junctions in the follicular epithelium and demonstrate an extracellular route whereby materials carried in the circulation may reach the oocyte without passing through the cytoplasm of follicular cells.

ISSN:0022-104X    

DOI:10.1002/jez.1401790307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractFull‐grown oocytes ofRana pipienswere dissected out of the follicles and induced to undergo germinal vesicle breakdown (GVBD)in vitroby progesterone treatment. When the progesterone treatment was carried out after displacing the germinal vesicle (GV) from the animal half to the vegetal half by centrifugation (200–400 × G for 10 minutes), a considerable delay of GVBD took place although all the GVs eventually broke down. GVs displaced near the vegetal pole frequently migrated towards the animal pole and gave off a polar body in the equatorial zone of the oocyte. When an oocyte was tightly constricted along the equatorial line with thread so that the migration of the GV was prevented, the frequency with which the GV broke down in the vegetal half was considerably decreased depending on the tightness of constriction. The ooplasm in the animal and vegetal halves of the progesterone‐treated oocytes was tested for GVBD inducing activity by injecting it into untreated oocytes which contain an intact GV. It was found that the ooplasm from the vegetal half induced GVBD in the recipients with a lower frequency than that from the animal half. To localize the GVBD inducing activity in the ooplasm, oocytes were centrifuged after progesterone treatment at the interface between Ringer's solution and Ficoll solution. The GVBD inducing activity of the ooplasm of the animal pole was increased after removal of yolk and pigment granules by a brief centrifugation (4000 × G for 5–10 minutes). Prolonged centrifugation (4000 × G for 2 hours) brought about stratification of the ooplasm. From the centripetal to the centrifugal side, five layers were distinguished: oil cap, fluid hyaline ooplasm, gelatinous hyaline ooplasm, pigment granules and yolk. The highest activity of GVBD induction was found in the hyaline ooplasm. Based on these results, a mechanism of the GVBD induction in the frog oocyte is

ISSN:0022-104X    

DOI:10.1002/jez.1401790308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractThis study was planned to determine the neuromuscular basis of the very rapid strike movement, lasting only 5–10 ms, used by mantis shrimps to capture prey or defend themselves. The raptorial second thoracic append‐ages which are responsible for the strike action are unfurled by four muscles in the merus, two extensors and two flexors. All were found to be specialized for slow not fast contraction. The largest extensor muscle has a twitch time of 400 ms, reaches peak tetanic tension in 700 ms and takes one second to relax completely from this. It receives two “slow” and one “fast” motor axons distributed uniformly throughout the muscle. An overshooting spike occurs in each muscle fiber from the first activation of a train in the fast axon, but many seconds must elapse before the first muscle fiber will again respond with a spike. The smaller, medial extensor receives one fast axon which may give rise to overshooting spikes and an inhibitor whose effects appear to be minor; its muscle fibers are only weakly electrically excitable. The contraction and relaxation rates are slow, as are those of the medial flexor which receives two slow axons. The lateral flexor is divisible into two parts; a proximal region comprised of electrically passive fibers innervated solely by a slow axon and a distal region of spiking fibers innervated by a fast axon. The rapid strike action is explained not in terms of the rapid contraction of these muscles but in their operation of a mechanical device in the form of a “click‐joint,” des

ISSN:0022-104X    

DOI:10.1002/jez.1401790309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

摘要:

AbstractThe ultrastructure of some muscle fibers of the five physiologically different motor units operating the strike of the mantis shrimp were studied by electron microscopy. The distal portion of the lateral flexor was found to have the shortest sarcomere length (4.3 μm), the densest, most complex sarcoplasmic reticulum, the largest number of dyads per unit cross‐sectional area and the smallest filament cluster (“fibril”) size. The proximal portion of the same muscle differs from it mainly in having a less well‐developed reticulum and a large filament cluster size.The remaining muscles have longer sarcomere lengths: 5.3 μm for the medial flexor, 7.8 μm for the lateral extensor, and 6.0–10.2 μm for the medial extensor, as well as a weakly‐developed sarcoplasmic reticulum and fewer dyads per unit cross‐sectional area.These data were compared with contraction and relaxation times of the units and showed that the rates of both contraction and relaxation are lower the greater the A band or true relaxed sarcomere length. For fibers of equal A band length, faster rates were found to be associated with a more extensive sarcoplasmic reticulum, giving reduced filament cluster size, as well as with a large

ISSN:0022-104X    

DOI:10.1002/jez.1401790310

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY

ISSN:0022-104X    

DOI:10.1002/jez.1401790301

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1972

数据来源: WILEY