ZOOLOGY AND BOTANY^ MICEOSCOPY, ETC. 217 



New Gymnosomatous Pteropod.* — M. P. Pelseneer recognizes four 

 families of known gymnosomatous Pteropods — Pneumodermatidge for 

 Pneumodermon, Dexiohranchxa, and Spongiohrancheea ; Clionidee for Clione ; 

 HalopsychidsB for Halopsyche ; and ClionopsidaB for CUonopsis. The new 

 genus — NotohrancJisea — which he now describes, must be placed in the fifth 

 family of Notobranchaeid£B ; in it the body is contracted behind, and presents 

 only a dorsal branchia, formed by three crests, of which the dorsal alone 

 is fringed. Anterior and posterior lobes of the foot long and narrow, the 

 former free in their posterior two-thirds. N. MacBonaldii sp. n. was taken 

 off Carolina, and measures 8 mm. in length. M. Pelseneer considers that 

 the Gymnosomata have been derived from the Aplysians, and that the least 

 specialized genus is Dexiohranchsea, with lateral branchiai ; Pneumodermon 

 is greatly complicated by the posterior branchia having four crests radiating 

 from the original ring ; CUonopsis shows retrogression, and Clione is appa- 

 rently derived from NotohrancJisea. 



Embryology of Prosobranch Gasteropods-f — Dr. J. P. McMurrich 



adds some additional facts to his previous contributions J on the subject. 



He finds corrosive sublimate and alcohol the best fluids for preservation. 

 Perenyi's fluid caused excessive swelling and distortion of the eggs con- 

 taining much yolk. 



He describes the egg-capsules of Fulgur carica, Fasciolaria tulipa. 

 Purpura floridana, and a species of Crepidula. 



1. The ovum and nutrition of the embryo. — Each capsule of Fulgur 

 contains 12 or 14 large eggs, imbedded in a large quantity of albuminous 

 substance, and containing much yolk. The reactions of the albumen showed 

 it to be a proteid. In the case of Fulgur, all the eggs develope ; but such 

 is not the case in the other forms, where only a few out of numerous eggs 

 develope, the rest serving as food. This breaking down is not due to non- 

 fertilization, but to the quantity of yolk being too small for the number of 

 eggs. He traces a series of stages in the proportional number of eggs 

 which develope, and concludes that some change in environment has ren- 

 dered it desirable for the eggs to remaiii longer in the capsule than their 

 ancestors did. He gives a summary of observations on this head. 



2. Segmentation and formation of germinal layers. — At the earliest stage 

 the polar globule, which is single in Fulgur, was already formed, and con- 

 tained yolk-granules. The ovum elongates, divides transversely into two 

 equal parts, through the polar pole. A second division gives four equal 

 spheres. Then, at the polar pole, an aggregation takes place from each of 

 these, which gets nipped off to form four micromeres, which are completely 

 protoplasmic. No further division takes place in the macromeres, which 

 gradually fuse ; but new micromeres arise partly from these, and partly 

 from the micromeres. At a certain stage a peculiar elevation takes place in 

 three of the macromeres, which is coincident with the first appearance of 

 the mesoderm, in the fourth macromere. Ultimately epibole becomes 

 complete, except for the blastopore. 



Then follow several pages devoted to theoretical questions. From the 

 presence of a single polar body in Fulgur, Dr. McMurrich considers that 

 the relative amount of protoplasm and yolk influence the formation of these 

 bodies, which may explain their usual absence in Crustacea. After a brief 

 review of the various modes of segmentation in the invertebrate phyla, he 



* Bull. Sci. Dep. Nord, ix. (1886) No. 6. Of. Ann. and Mag. Nat. Hist., xix. 

 (1886) pp. 79-80. 



t Stud. Biol. Lab. Johns-Hopkins Univ., iii. (1886) pp. 403-45 (4 pis.). 

 % See this Journal, 1886, p. 583. 



1887. Q 



