ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 789 



B. Asexual reproduction. 



a. Fission, with repair. 

 /?. External gemmation from a single arm. 

 In certain cases heteractinism would appear to be due to increased 

 activity, consequent on inflammation. 



Circulatory Apparatus of Regular Echinoids.*— R. Koehler de- 

 scribes the presence of two circular circumoesophageal vessels, and 

 of two vessels in each ambulacral zone ; he also proves the complete 

 independence of the nervous and circulatory systems, and finds that this 

 last communicates with the excretory organ by means of the sand- 

 canal. The sand-canal is not simple, but is really formed of two, 

 which are closely connected together; the only one which has as yet 

 been described is independent of the ovoid gland of Perrier, or the 

 organ of excretion, while the other is connected with it. Transverse 

 sections of the sand-canal reveal the presence of one tube regularly 

 lined by epithelium, and of another whose lumen is partly filled by 

 bars of connective tissue which form a delicate reticulum supporting 

 protoplasmic cells. The second canal, when it reaches the ovoid 

 gland, increases in diameter, the partitions in its lumen become more 

 numerous, while the gland itself consists, as in irregular Echinoids, 

 of trabecule of connective tissue which are very delicate, and have 

 their alveoli filled with protoplasm and pigmented bodies. The two 

 circumoesophageal vessels communicate with one another at the level 

 of the Poliau vesicles. 



Structure and Development of Ophiuroids.f — K. Nicolas 

 Christo-Apostolides has at length published, in the French language, 

 the full text of his memoir on Ophiuroids, with six plates. While 

 availing himself of modern aids to histological research, he enjoyed 

 the advantage of a copious supply of living specimens, and he rests 

 his claims on the circumstance that he made good use of these as 

 well as of preparations. 



Five genera, including eight species, were examined. Nut much is 

 said of the skeleton and body- wall in the adult animal. The soft parts 

 are minutely analyzed. J The simple sac-like alimentary canal, without 

 mesenteries or free glandular appendages, consists of four separate 

 layers — (a) an internal ciliated epithelium, (b) a brown layer with long 

 (muscular) fibres, (c) a cellular (secretory) layer and (d) an investment 

 of connective tissue. In this last are found peculiar triradiate calcareous 

 spicules, the free ends of whose rays become again triradiate. There is 

 a distinct, though short, oesophagus. The larval form has an anus, 

 wanting in the adult. 



Imprisoned brittle-stars, eight or ten days after being captured, 

 show an opening in the middle of the back. Our author believes 

 that, in consequence of starvation, a sinking of the dorsal wall takes 

 place ; this, with the central portion of the gut, becoming engaged 

 among the five oral pieces, is bitten off as a substitute for food. 



* Comptes Eeudus, xcv. (1882) pp. 459-61. 



t Arch, de Zool. Expe'r. et Gen., x. (1882) pp. 121-224. 



X See this Journal, i. (1881) pp. 466 and 606 ; ante, p. 199. 



