ZOOLOGY AND BOTANY, MICKOSCOPY, ETC, 309 



peculiar stellate cells with ramifying processes appear between the 

 external and internal chitinous layers, and play an essential part in the 

 deposition of lime in the shell. 



Annulata. 



Structure of an Archiannelid.*^E. S. Goodrich describes Nerilla 

 antennata 0. Schmidt, a minute Syllid-like worm about 1 • 5 mm. in 

 length when full grown, which is the most Polychaete-like of all the 

 Archiannelids, and seems to occupy a central position among the widely 

 differing genera {Histriobdella, Dinophilus, Protodrihis, Polygordius, etc.) 

 of that group. Its affinities are perhaps more especially with the two 

 first of these genera. Many Ch^etopod characters are preserved. The 

 egg^ are laid in transparent capsules, development is direct, and the 

 young emerge as small worms with only one median tentacle and about 

 five seo:ments. 



■'B' 



Cell-division in Polychaets and Trematodes.f — A. Dehorne has 

 made a detailed study of homeotypic cell-division in the epidermis and 

 spermatogonia of Sabellaria and in the spermatogonia of the liver-fluke, 

 and of heterotypic division in the spermatogenesis of Sabellaria, Opliryo- 

 trocha, Lanice, and the liver-fluke. He maintains the view that the 

 chromosome is always a paired structure ; that it does not consist of 

 linin and chromatin, but of one homogeneous substance ; that reduction 

 is not brought about by division of chromosomes, but by a quite peculiar 

 process which destroys the unity of the nucleus ; and reaches many other 

 remarkable conclusions for which we must refer to the elaborate and 

 finely illustrated paper itself. 



New Parasitic Polychset. J — F. A. Potts describes Parasitosyllis g. n., 

 a minute Syllid, 5 mm. long, which he found in a collection made by 

 Crossland at Zanzibar. Individuals were found Kving on both Polych^et 

 and Nemertine worms, fixed by the permanently protracted pharynx which 

 is inserted in the body-wall of the host and so intimately intergrown 

 with its tissues that it was impossible to detach the parasites from their 

 prey (save in the case of the soft-bodied Nemertine) without breaking 

 off the pharynx from the rest of the body. Potts compares Parasitosyllis 

 with Eisig's Ichthyotomus, another ectoparasitic Polych^et. It occurs on 

 the eel, firmly attached by its pharynx. But the two genera differ rather 

 widely in structure and habits. 



Sex Determination in Dinophilus. § — Cresswell Shearer has investi- 

 gated this in Dinophilus gyrociliatus, a minute primitive Annelid which 

 has pronounced sexual dimorphism, the males being rudimentary. Two 

 kinds, large and small, respectively female-producing and male-producing, 

 are normally laid together in one capsule. In a few days the small eggs 

 give rise to the rudimentary males, which are full grown and sexually 

 mature at the time the females are ready to leave the capsule. The 



* Quart. Journ. Micr. Sci., Ivii. (1912) pp. 397-425 (4 pis.). 



t Arch. Zool. Exper., ix. (1911) pp. 1-175 (14 pis.). 



X Proc. Cambridge Phil. Soc, xvi. (1912) pp. 409-13 (2 figs.). 



§ Quart. Journ. Micr. Sci., Ivii. (1912) pp. 329-71 (5 pis. and 5 figs). 



