190 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Anatomy of Pleurotomaria.* — MM. Bouvier and Fischer have been 

 enabled to dissect a specimen of P. quoyana obtained by the ' Blake,' and 

 prefix to their paper a general account of the existing species, of the 

 specimens hitherto obtained, which in most cases have been shells only, 

 and of our previous knowledge of the structure, which is very scanty. 



They find that the radula differs markedly from that of the other 

 Scutibranchia, especially in the absence of a distinct division into cen- 

 tral and lateral regions, for there is a gradual transition from central to 

 lateral teeth. There are also rema'kable and characteristic triangular 

 and brush-shaped teeth. The eye is a simple cup open to the exterior. 

 In the otocysts there are a large number of simple otoliths of very un- 

 equal size — a very primitive character. The nervous system in essentials 

 resembles that of the Trochidaa and Fissurellidse, but in its minor details 

 seems to recall that of the Amphineura. Further, it appears to shed 

 light on the vexed question of the origin of the pedal nerves, and the 

 relation of pedal and pallial ganglia in Gastropods in general. In 

 Pleurotomaria the pallial panglia appear to be absent, but in reality lie 

 side by side with the pedal. A detailed comparison of this condition 

 with those obtaining in other Gastropods leads the authors to the con- 

 clusion that the " pedal " nerves, so-called, of all Gastropods are of 

 mixed pedal and pallial origin, and that the " pallial " ganglia are 

 merely an anterior portion of the true pallial ganglia, the posterior 

 portion being fused with the pedals. In Pleurotomaria this anterior 

 separation of a part of the pallial ganglia does not occur, and a deep 

 groove separates the pedal from the undivided pallial ganglion at each 

 side. Adopting this view of the homologies of the Gastropod ganglia, 

 the authors discuss in detail the probable evolution of the Prosobranch 

 nervous system, showing how the condition seen in Pleurotomaria may be 

 regarded as transitional between that of the Amphineura and the Proso- 

 branchs generally. The details of the argument cannot be rendered 

 clear without figures, but the general result is to suggest that Pleuro- 

 tomaria quoyana must be regarded as one of the most primitive of 

 Gastropods. 



Gonads and Nephridia of Prosobranchia.f — Prof. B. Haller criti- 

 cises Pelseneer's J recent paper on primitive Mollusca, and especially 

 the views expressed in it as to the relations of nephridia and gonads. 

 Haller's own views as to the phylogeny of the gonads of Mollusca are 

 based on the assumption — admitted by Pelseneer — that these were 

 originally paired organs, as they are in Chiton. In the alsence of a 

 connection between gonads and nephridia, however, Chiton shows a less 

 primitive condition than the simpler Gastropods, where the right 

 nephridium is connected with the reproductive organ. In both the 

 Monobranchiate and Cyclubranchiate Uocoglossa, according to Haller, 

 there is a ventral coelomic space divided into two by a sagittal mesentery. 

 Pelseneer, on the other hand, regards the right half of this space as a 

 part of the right nephridium, a view for which Haller believes there is 

 no evidence. According to him, in the Cyclobrauchiate Docoglossa the 

 gonad developes directly from the epithelium of the secondary body- 



* Bull. Mus. Cnmp. Zocl. Harvard, xxxii. (1899) pp. 193-249 (4 pis. and 6 figs.). 

 t Zool. Anzeijr., xxiii. (1900) pp. «J1— €. 

 X Bull. Acatl. Roy. Belgique. lvii. (1899). 



