588 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the southern hemisphere, 20 species are common to the British coasts, 

 5 species only are known also from the Mediterranean. On the whole 

 the Polyzoa do not lend support to Sir John Murray's bipolar hypothesis, 

 and the author considers that a critical survey greatly reduces the num- 

 ber of species supposed to be common to the Arctic and Antarctic, and 

 absent from the intervening areas. 



Development of Phoronis.* — Prof. Louis Eoule states that a com- 

 plete account of this development based on his own researches is in the 

 press, and that his results differ from those obtained by Masterman f 

 in some respects. The special point of difference is in regard to the 

 development of the mesoderm, which Masterman states has an entero- 

 coelic origin. The point is of importance, as Masterman found a striking 

 correspondence between Enteropneusta and Phoronis in regard to the 

 origin of this layer. Eoule's own observations on fresh material confirm 

 Metschnikoff's previous statements that the mesoderm has a mesenchy- 

 matous origin. He further holds that, even apart from his own observa- 

 tions, Masterman's figures show that his preparations were not in good 

 condition, and his conclusions not warranted by the evidence at his 

 disposal. While denying the existence of any resemblance between the 

 development of Phoronis and that of Enteropneusta, Eoule agrees with 

 Masterman in regard to the existence of a rudiment of a notochord in 

 the Actinotrocha. 



Echinoderma. 



Rearing of Echinoid Larvae.J — Prof. E. W. Macbride has, after 

 much experimenting, been ahle to rear Echinus larvae in numbers through 

 the metamorphosis. His method is detailed, but its general interest is 

 the light which it throws upon the physiology of development. The first 

 condition for a successful experiment is found to be the use of full-sized 

 and perfectly ripe individuals of both sexes as sources of eggs and 

 sperms. Next it was found that water must be obtained from the open 

 sea, not inshore, and must be changed frequently throughout the course 

 of development. The extent of change necessary varies for each season 

 according to the amount of vegetable plankton present, and generally it 

 would appear that the necessity for the frequent changes is due to want 

 of food rather than to deficient oxygen. Finally, an interesting point is 

 that in the most successful cultures only a proportion of the larvae are 

 sufficiently healthy to survive, and an important part of the method is 

 " to allow natural selection to weed out the weaker," and after the selec- 

 tive process has taken place, to devote attention only to the healthy 

 forms. 



Hermaphroditism and Parthenogenesis in Echinoderms.§ — C. 

 Viguier makes an important note on this subject. Hermaphroditism 

 is well known in Synaptids ; it has also been proved in Amphiura 

 squamata and Asterina gibbosa. But while the representatives of Asterina 

 at Eoscoff and Banyuls show a protandrous hermaphroditism, those at 

 Naples do not. Cuenot found at Eoscoff an Asterias glacialis which was 

 hermaphrodite and capable of self-fertilisation. Viguier notes a similar 



* Zool. Anzeig., xxiii. (1900) pp. 425-7. t Cf. this Journual, ante, p. 4GS. 

 % Journ. Mar. Biol. Ass., vi. (1900) pp. 94-7. 

 § Comptes Kendus, cxxxi. (1900) pp. 63-0. 



