120 CURRENT LITERATURE. 



8th century ; and (3) the last 100 years. This third era is divided into two 

 periods: — (a) pre-Danvinian — characterised by the application of anatomy to 

 systematic work (this might, in our opinion, have well been termed the Cuvierian' 

 period) ; and (b) the post-Darwinian- — characterised by the morphological and 

 other investigations pursued in the light of the doctrine of descent. 



These investigations have given rise to the publication of numerous antagonistic 

 or supplementary schemes of Molluscan classification, and Simroth gives a very 

 useful series of synopses of the more important of these schemes. We eagerly 

 look forward to the succeeding numbers of this new edition of Bronn's invaluable 

 work. — W. G. 



Tomlin, B. — Rissoa menibranacca, Adams. Brit. Nat., 1S92, p. 257. 



STRUCTURE AND DEVELOPMENT. 



Andre Emile. — Sur les teguments du Zouites cellar his. Zool. Anz., 1893, xvi., 

 pp. 39-40, one figure. 

 The author briefly describes the occurrence of a iiumber of peculiar little pits 

 in the skin on the right side (only) of the body in Z. cellarius. They are 

 invaginations of the ectoderm, either simply pyriform or slightly branched ; but 

 their function is altogether uncertain. 



Collinge, Walter E. — On the Absence of the Male Reproductive Organs in two 

 Hermaphrodite .Molluscs. Journ. Anat. and Phys., 1893, pp. 237-8. 



Erlanger, R. v. — Mittheilungen iiber Bau und Entwicklung einiger marinen 

 1'rosobranchien. I. Ueber Capulus hungaricus. Zool. Anz., 1892, xv., 

 pp. 465-468. 



The author finds that Capulus hungaricus, like most Monotocardia, is pro- 

 vided with a " nephridial gland"; and he has attempted, by an embryological 

 investigation upon this form, to ascertain the truth of R. Perrier's hypothesis, 

 that the nephridial gland is the homologue of the definitive left (primitive right) 

 nephridium of the Diotocardia and Ileterocardia. 



It cannot, according to Erlanger, be the homologue of the primitive right 

 nephridium, because strong evidence tends to show that it is the primitive right 

 nephridium which retains its function in Prosobranchs provided with only one 

 nephridium. It is quite possible, however, that the gland corresponds to the 

 primitive left nephridium ; in which case a pair of nephridia, or at least a pair of 

 nephridial rudiments, should be demonstrable in the embryos of such forms as 

 Capulus, which possess a nephridial gland and a single nephridium in the adult. 



The chief observations made by the author are as follows : — In the segmen- 

 tation of the ovum a typical 4-cell stage occurs. The mouth appears to correspond 

 to the part of the blastopore which is last kept open. From the point where 

 stomodaum meets archenteron a ccelomic pouch (really paired ?) projects on each 

 side. This breaks down, and pericardium and nephridium are derived from 

 a common rudiment which is built up from the mesoblast on the right side of the 

 still symmetrical larva. This rudiment migrates to the left and dorsally ; and 

 soon differentiates into pericardium (in which the heart develops) and nephridium. 

 The latter is an unpaired epithelial sac. The actual origin of the " nephridial 

 gland " could not he observed ; but the author, failing to establish Perrier's 

 hypothesis, inclines to the view that the gland is a differentiation of the tissue of 

 the nephridium, or an ectodermal gland-formation, which has secondarily fused 

 with the nephridium. 



In the general development of gut, mantle, and shell, Capulus resembles 

 Bythinia. Internal Umieren are absent ; a large pale nucleated ectoderm-cell on 

 each side behind the velum represents the so-called external Uriiiere. Larva 

 transparent ; velum highly developed ; foot provided with an operculum (absent 

 in adult); shell wound as in other veligers (unwound and symmetrical in adult). 



