ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 487 



fails to divide and only one division centre is obtained. The author 

 proceeded to study the cleavage of these monaster eggs, and was led to 

 the general conclusion that at the time of fertilization progressive 

 changes, which go on independently of the nucleus and of cleavage, are 

 initiated in the cytoplasm of the eggs, and that these changes determine 

 the position of the spindles in the egg and consequently in the blasto- 

 meres. 



The monaster eggs were isolated and followed through their cleavage. 

 At the time when the control eggs were in the sixteen-cell stage, one or 

 more small cells appeared in the cleaving monaster eggs. These were 

 usually in the eight-cell stage at this time. In order to determine the 

 cause of micromere formation, eggs were treated with potassium cyanide 

 and phenyl urethane, or were kept at a low temperature after fertiliza- 

 tion. By treating the eggs with phenyl urethane it was possible to 

 throw the micromere formation into the two-, four- or eight- cell stage. 

 The evidence goes to show that differentiation, in so far as the formation 

 of the micromere is concerned in the sea-urchin egg, is dependent upon 

 cytoplasmic oxidation, the nucleus and the cleavage process playing no 

 direct part here. 



Ccelentera. 



Comparative Anatomy of Some British Actiniae.* — Oliven M. 

 Rees describes Sagartia miniata, S. ornata, S. sphyrodeta, Anthopleura 

 alforiU, Uorynactis virMis, and the rare Aureliania regalis, giving details 

 as to the transverse sections of body-wall, mesenteries and tentacles. 



Porifera. 



Gemmules of Ficulina and otfier Sponges. f— Karl Midler has 

 made a study of gemmules in Ficulina ficas and some other sponges. 

 A list is given of those sponges in which the occurrence of true gemmules 

 has been proved, and of those in which gemmule-hke bodies occur. In 

 Ficulina they usually occur in a dense layer next the substratum or the 

 shell on which the sponge grows. In some cases they occur freely in 

 the body in crowded roundish clumps ; they are never isolated from one 

 another' as in Spongillidse. It is often easy to separate off the sponge 

 from the substratum, leaving the gemmule layer attached. The gem- 

 mules vary greatly in size and shape. Each consists of a cellular body 

 and a capsule of two concentric spongin layers without a pore. The 

 capsule is strengthened by spinose microrhabda or amphidiscs. The 

 internal cells are polygonal, compressed and laden with yolk-material. 

 A gemmule arises from a collection of archasocytes, into which more 

 elements migrate. There is a gradual differentiation into internal yolk- 

 cells and a double layer of follicle-like epithelial cells round the circum- 

 ference. The latter secrete the membrane. The microscleres, micro- 

 rhabda and amphidiscs, are not formed from the epithelial cells but in 

 normal scleroblasts outside the gemmule. They are transported to the 



* Journ. Marine Biol. Assoc, x. (1915) pp. 521-64 (16 figs.). 



t Wiss. Meeresuntersuch. Kiel, xvi. (1914) pp. 289-313 (4 pis. and 10 tigs.). 



