508 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The first shares only a little in the formation of the thymus, but 

 comes afterwards into connection with the ear, forming the tympanic 

 cavity and auditory tube. From II. and III. arises the main part of the 

 thymus. From IV. there also arises an epithelial body, which sub- 

 sequently atrophies. The sixth forms on the left side the supraperi- 

 cardial corpuscle of van Bemmelen. 



Development of Spleen in Tropidonotus natrix.* — Emil Glas finds 

 that in this form the spleen originates from the endoderm. It arises, 

 together with the dorsal pancreas, from an evagination on the dorsal 

 surface of the duodenum. Originally it is structurally similar to the 

 pancreas, consisting like it of tubular glands, so that it is legitimate to 

 speak of a hep>atopancreas and a lieno-pancrcas. The duct of the lieno- 

 pancreas unites with that of the dorsal pancreas to form a common duct, 

 which opens into the gut close to the common opening of bile-duct, 

 cystic duct, and ventral pancreatic duct, and may be called the ductus 

 pancreatico-lienalis. In the youngest stages this duct is entirely dorsal, 

 and its opening is opposite to that of the ventral pancreatic duct. Later 

 it approaches more and more closely to the bile-duct, until it finally 

 unites with it, and opens with it on the ventral surface of the gut. 



Development of Egg in Mabuia multifasciata. f — Dr. J. H. F. 



Kohlbrugge has been able to trace the development of the egg in this 

 viviparous skink from the first stage until fertilisation. The primordial 

 eggs show a reticular cytoplasm and a vesicular nucleus, whose margin 

 consists of chromatin radiating out into the cytoplasm. As the cells 

 increase in size, karyosomata appear in the nucleus, and smaller micro- 

 somata in the cytoplasm. Meanwhile, the future follicular cells have 

 arranged themselves around the egg to form an investment, and individual 

 cells become free and pass into the egg-substance. While this is going 

 on, nucleoli, often vacuolated, appear within the egg-nucleus, and the 

 nucleus itself becomes separated by a clear space from the cytoplasm. 

 The egg unites with the surrounding inner follicular cells to form a 

 syncytium, and yolk-formation begins. This occurs in two regions of 

 the egg — at the margin under the influence of the follicular cells, and 

 centrally under the influence of the nucleus, both karyosomata and 

 microsomata forming yolk-spherules. The yolk-nuclei of other in- 

 vestigators the author believes to be the nuclei of dissolved follicle cells 

 or nucleoli discharged from the egg-nucleus. 



Germ-layers of Podocnemis madagascariensis.J — Dr. A. Voeltzkow 



has studied the germinal discs in a number of eggs of this fresh-water 

 tortoise, in order to settle the disputed questions connected with the 

 very early stages of development. He finds that an outer and an inner 

 crescentic groove can be distinguished. The outer or primitive cres- 

 cent is the beginning of the primitive plate, and is the homologue of 

 Roller's crescent in the chick, and Will's primitive crescent in Platy- 

 dactylus and Testudo. The inner crescentic groove is identical with the 

 mesodermic crescent, and with Kupffer's crescent. There are no inter- 

 mediate plates, no diverticula of the ccelom, no formation of folds ; but 

 the common endoderm splits into enteroderm and mesoderm ; the median 



* SB. Akad. Wiss. Wien, cix. (1900) pp. 265-99 (3 pis.). 



t Arch. Mikr. Auat., lviii. (1901) pp. 376-410 (3 pis.). 



X Abh. Senckeuberg. Nat. Ges., xxvi. (1901) pp. 275-310 (4 pis. and 8 figs.). 



