ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 315 



clinum, the distinction of species is beset with great difficulties. ^ A 

 remarkable fact is the total absence of members of the family Ascididse, 

 which appear to be rare in the Pacific Ocean. Among the social forms 

 a new species occurs, named by the author Ecteinascidia diligens, which 

 differs from the other members of the genus, and indeed from the other 

 members of the Clavellinidae, in possessing an entire dorsal lamina in 

 place of dorsal languets. The author does not however believe that 

 the condition of the dorsal lamina is of sufficient importance to justify 

 the erection of a new genus, for the genus Cynthia exhibits both condi- 

 tions. The new species is further remarkable for a large brood-chamber 

 which appears when numerous embryos are present. 



Balanoglossus as a Generic Name. * — Dr. S. F. Harmer considers 

 that Spengel was not justified by the laws of zoological nomenclature 

 in retaining the name Balanoglossus in his Monograph in a restricted 

 sense, for it is merely a synonym for Ptychodera. Dr. Harmer proposes 

 the name Balanocephalus as a generic name for the species included by 

 Spengel in the old genus. The type species would then be B. kupfferi 

 v. Willemoes Suhm. 



INVERTEBRATA. 



Mollusca. 

 y. Gastropoda. 



Cell-lineage in Aplysia.f — Dr. D. Carazzi has followed the earlier 

 stages of development in Aplysia limacina L., with special reference to 

 the spiral cleavage and the cell-lineage. He finds that oviposition 

 occupies a period of 4-5 hours, the calculated number of eggs laid at 

 one time being about three millions. Fertilisation is internal, but 

 maturation does not occur till after deposition, the spermatozoon mean- 

 while lying inert within the ovum. The first segmentation furrow 

 appears from four to five hours after deposition. The blastomeres are 

 markedly unequal, and the author was enabled to study in detail the 

 remarkable phenomena associated with their formation, and to correct 

 certain errors of previous observers. The exact manner of formation 

 cannot be made clear without figures. In regard to the further history 

 of segmentation and of the resultant blastomeres, perhaps the most 

 important point is the origin of the mesoblast from the division of the 

 cell called 4 d in Conklin's nomenclature. This method of origin of 

 the mesoblast has now been described among the Mollusca in fifteen 

 Gastropods, two Lamellibranchs, and Isclmochiton among Amphineura. 

 The author believes that it will also be found to occur in other Mollusca, 

 when embryologists become more conscious of the necessity of making 

 observations on entire eggs instead of relying wholly on sections, and 

 cease to allow their work to be dominated by the gastrula theory. The 

 paper also includes a brief general discussion of the origin and signi- 

 ficance of the mesoblast. 



Morphological Notes on Tectibranchs.* — Dr. G. Mazzarelli dis- 

 cusses the structure of the liver, the reno-auricular communication, 



* Proc. Cambridge Phil. Soc, x. (1900) pp. 190-1. 



t Anat. Anzeig., xvii. (1900) pp. 77-102 (6 figs.). 



X Biol. CentralbL, xx. (1900) pp. 110-20 (figs. 14-24). 



