96 RECORD OP CURRENT RESEARCHES RELATING TO 



wliicli these masses are composed, are gradually made to run together into 

 an equatorial ring. As development goes on the cells separate again, 

 and resume their amoeboid movements ; some take on the function of 

 skeletogenous cells, producing the skeleton as a cuticular secretion ; 

 others go to form the circular musculature of the foregut, the midgut 

 and hindgut remaining devoid of muscle ; and the remainder go to 

 form suspensory cells connecting the alimentary canal with the body- 

 walls. 



3. The Gastrula. — Invagination takes place at that pole where the 

 cells are largest ; a tubular cavity is produced, the aperture of which 

 (blastopore) becomes the larval anus. It was stated by Krohn that the 

 blastopore served for the ingestion of nutriment until the permanent 

 mouth was formed ; but according to Selenka this is impossible, as the 

 cilia of the archenteron all work outwards. 



From the blind end of the archenteron two lateral outpushings 

 arise, which, with the actual extremity of the archenteron connecting 

 them, become segmented off as a single sausage-shaped sac, the vaso- 

 peritoneal vesicle. This then divides into two symmetrical halves, of 

 which one is the right peritoneal sac, while the other subsequently 

 divides into the left peritoneal sac and the rudiment of the ambulacral 

 system. 



When metamorphosis takes place the larval mouth disappears, but 

 the larval anus persists as the adult vent. 



Coelenterata. 

 Histology of Ctenophora.*— Dr. Carl Chun, of Leipzig, has a 

 short paper on this subject, consisting mainly of adverse criticisms 

 of the work of Buekers and Eimer. The point of chief interest in 

 the paper is the description of the tactile papilla discovered by the 

 author on the aboral region of Cestus Veneris. It consists of a number 

 of globular vesicles with granular contents, and enclosing crystals, 

 probably of leucin, arranged in a radiate manner ; amongst these 

 vesicles occur cells bearing tactile hairs. Both these latter and the 

 vesicles are develoj)ed from ordinary polygonal ectoderm-cells. 



Development of the Alcyonidse.f — Professor Kowalevsky has 

 lately been engaged in the examination of the larvfB of Sympodium 

 coralloides. The youngest forms' examined were provided with an 

 ectoderm of cells somewhat flattened ; these became in time more 

 cylindrical and smaller, until in the completely matured larva the 

 ectoderm consisted of a number of closely appressed, long, fine cells, 

 the nuclei of which were so placed as to give it the appearance of 

 cylinder epithelium. The gastric cavity was formed by the invagina- 

 tion of the free pole, and meantime the ectoderm increased considerably 

 in thickness, and gave rise to an intermediate, transparent, and gela- 

 tinous tissue. The cells, losing their cylindrical form, became 

 elongated and spindle-shaped, or stellate, till they formed several 

 rows of cells, separated by a gelatinous tissue. The author is of 

 opinion that the preceding account details the history of the origin of 

 the mesoderm. In examining the formation of the sjiicules which 

 * 'Zool. Anzeiger,' ii. (1879) p. 329. f IWd., p. 491. 



