556 SUMMARY OF CURRENT RESEARCHES RELATING TO 



accumulation in the cytoplasm of metaplastic material in preparation for 

 yolk-formation. This is accompanied by an increase in the basophile 

 staining capacity and fluid consistence of the cytoplasm. The process 

 of yolk formation, that is the actual appearance of the definitive yolk- 

 spherules, is unaccompanied by increased nuclear or nucleolar activity, 

 and consists simply in the rapid and automatic conversion of the 

 accumulated material into a form sufficiently stable to survive the period 

 of quiescence which succeeds the completion of the growth of the egg. 



The oocyte constitutes an osmotic system, of which the cell-wall 

 forms an outer, the nuclear membrane an inner semi-permeable mem- 

 brane. The accumulation in the cytoplasm of soluble substances in 

 preparation for yolk-formation causes an increase in the osmotic 

 intensity at the outer membrane, and a corresponding decrease of that 

 at the inner. The loss of turgescence which thus results permits of the 

 assumption of an irregular form during fixation. 



Up to the expansion due to the formation of the definitive yolk- 

 spherules, the size of the germinal vesicle shows a close relation to that 

 of the egg, and is determined when equilibrium is established between 

 the rate of diffusion of nutritive substances through the nuclear mem- 

 brane on the one hand, and the requirements of the chromatin on the 

 other. 



Nervous System of Asteridge.* — R. Meyer deals with the finer 

 structure of the nervous system in Asteridge, describing the radial 

 system, the cuticula, the covering or support cells (Stiitzzellen), gland-, 

 sense-, and ganglion-cells in Asterias rubens. With reference to the 

 " enteroccel nervous system," described by Cuenot, as existing in the 

 dorsal peritoneal epithelium in A . glacialis and other starfish, the author 

 expresses doubt. He failed to find it in A. rubens, and points out that 

 Cuenot himself could not observe it in Aster ina. On account of these 

 facts he is inclined to question the existence of an enteroccel nervous 

 system. 



Coelentera. 



Sexual Dimorphism in Aglaophenia.f — H. B. Torrey and Ann 

 Martin find that, in those species bearing both closed and open corbulae 

 which they have examined (A. diegensis Torrey, A. plnma (Linn.), A. 

 siouthionides Murray, and A. inconspicua Torrey), the female gonophores 

 are contained solely in those corbulae which have completely fused 

 leaflets (closed) ; the male in those where the leaflets are more or less 

 free from one another (open). They therefore consider it highly 

 probable that other species of Aglaophenia, and perhaps even other 

 genera, may show sex characters of a similar nature in their phylac- 

 tocarps. 



Structure of Isis Hippuris.J — J. J. Simpson, in view of the fact 

 that the genus Isis has hitherto been but imperfectly described and 



* Zeitschr. wiss. ZooL, lxxxi. (1906) heft 1, pp. 96-144 (2 pis.). 



t Univ. California Publications (Zool.) iii. No. 4 (1906) pp. 47-52 (9 figs.). 



X Journ. Linn. Soc, xxix. (1906) pp. 421-33 (1 pi.). 



