ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 457 



Antarctic Isopods.* — T. V. Hodgson reports on a collection of 

 twenty-five species, some of which are new and interesting. Seven, 

 mostly assigned to new genera, have their eyes on enormous peduncles, 

 an entirely new feature among " sessile-eyed " Crustacea. Attention is 

 directed to the sexual dimorphism in Arcturidse. The male and female 

 of one species, Antarcturus frankUni, appear on one of the plates as two 

 species — quite markedly different. It was only when all the specimens 

 of both sexes (or, as it was thought, both species) came to be overhauled 

 that the error was noticed. Hodgson shows that Serolis comutus Studer 

 is merely the immature form of S. trilobitoides Eights. He expresses his 

 conviction that a very large proportion of the species of the South Polar 

 fauna have a circumpolar distribution. 



Twin Sacculina.f — M. Kollman describes a case of a twin Sacculina 

 betencouri on Portunus variegatus. There were two bodies, but one root- 

 system, and the internal state of the visceral masses pointed to a single 

 origin. The author speaks of this as polyembryony. 



New Ascidicolous Copepods. | — E. Chatton and E. Brement 

 describe the females of Aplostoma magellanica sp. n., from a Magellan 

 Synascidian, A. sacculus sp. n., from Diploxoma spongiforme Giard, and 

 Aplostoma hibemica (T. and A. Scott). They show that the generic 

 diagnosis, based on A. brevicauda, will have to be enlarged. The 

 characters that are most diverse are those which are most directly in 

 relation with the animal's mode of life (e.g. external form and structure 

 of appendages). Other characters, such as the ornamentation of the 

 vulva, or the nature of the apical plate, are very uniform. 



Annulata. 



Giant Nerve-cells and Fibres of Halla.§ — J. H. Ashworth gives a 

 detailed account of the giant cells which appear in segmental couples in 

 each of the anterior ganglia of this Polychsete, and of the giant fibres, 

 each of which, after leaving the giant-cell from which it arises, crosses 

 the cord to the opposite side and then turns gradually towards the middle 

 line of the cord and runs posteriorly. The contents of the giant-fibre 

 are the equivalent of the axis cylinder of an ordinary nerve-fibre, being 

 a direct continuation of the protoplasm of the giant-cell ; moreover, the 

 structure of the axis cylinder of the giant-fibre is very similar to that of 

 the axis cylinder of a medullated nerve-fibre, except that in the former 

 there is nothing comparable to the Ranvier's nodes of the latter. The 

 author gives a detailed description and beautiful figures of the minute 

 structure of cells and fibres, and compares those in Holla with those of 

 Aglaurides fulgida. A posterior set of giant-cells and fibres has not 

 been dealt with. 



Polychaets from the Atlantic adjacent to Ireland. || — R. Southern 

 defines two new 7 species of Travisiopsis, and records a number of 

 Alciopinge, TomopteridEe, and Typhloscolecidas. 



* National Antarctic Exped. (Nat. Hist.) v. (1910) Crustacea, No. ix. pp. 1-77 

 (10 pis.). 



t Arch. Zool. Exper., v. (1910) Notes et Revue, No. 2, pp. xxxvii-xl (1 fig.). 

 X Bull. Soc. Zool. France, xxxv. (1910) pp. 80-92 (5 figs.). 

 § Phil. Trans., Series B, cc, pp. 427-521 (G pis.). 

 || Ann. Nat. Hist., v. (1910) pp. 428-9. 



