624 SUMMARY or CURRENT RESEARCHES RELATING TO 



are all unipolar. In the central ganglia groups of very large cells 

 alternate quite regularly with other masses which are formed of much, 

 smaller cells. 



The muscles are composed of ribbon-shaped smooth fibres, disposed 

 like those of the non-striated muscles of higher vertebrates ; in each 

 fibre there is a rod-shaped nucleus. In the foot the muscles are very 

 regularly arranged, and form two external circular layers, within 

 which are some thirty longitudinal bundles. 



The digestive tube is clothed by a simple epithelium, which is in 

 some regions distinctly glandular, and in others ciliated; the liver 

 and the kidney are hollow pouches, the wall of which is a simple 

 glandular epithelium ; below the anus there is a pouch common to the 

 two halves of the kidney. 



The generative organs are filled by a compact mass of generative 

 products ; near the surface of the ovary there are young ovules, the 

 greater part of which is occupied by the nucleus, within which there 

 is a nucleolus composed of two very dissimilar halves. In the mature 

 ovum the double nucleolus disappears. M. Fol has not been able to 

 find the efferent genital canal which has been described by Lacaze- 

 Duthiers; the glands appear to him to empty themselves merely by 

 dehiscence into the pallial cavity, the renal gland, or, as is most 

 probable, by the anal gland. 



Nervous System of Fissurella.* — M. L. Boutau describes the 

 nervous system of Fissurella alternata and comes to a different con- 

 clusion from that arrived at by Ihering from an investigation of 

 F. maxima. In Fissurella, as in the typical nervous system of 

 Gasteropoda, there are two cerebroid, two pedal, and five asymmetrical 

 ganglia. There is, besides, a triangular nervous mass the morpho- 

 logical signification of which has been pointed out by Lacaze-Duthiers. 

 This triangle is a simple extension of the pedal and the two first 

 asymmetrical ganglia, which, being linked together, have acquired an 

 exceptional development and become drawn out. 



The nervous system of ParmopJiora is intermediate between that of 

 Haliotis and of Fissurella ; Mmarginula is likewise furnished with the 

 nervous mass above named and ranks between ParmopJiora and 

 Fissurella, for the coalescence of the pedal and asymmetrical centres is 

 carried in each animal a little less far than in the last-named type. 



Anatomy and Systematic Position of Halia priamus Risso.f — 

 M. J. Poirier gives a full description of the anatomical structure of 

 Halia priamus Eisso. With the exception of the operculum, which 

 is wanting, the greater number of the organs resemble in form those 

 of Buccinum. The formula of the radula is 1, 1, 1, not 1, 0, 1 as has 

 been erroneously stated. Hence its systematic position is no longer 

 with the Pleurotomidse where lately it has been placed, but with the 

 Buccinidse. 



Tectibranchiata of the Gulf of Marseilles.^— M. A. Vayssiere has 

 examined thirty-seven species of Tectibranchs ; they are all Opistho- 



* Comptes Rendus, c. (1885) pp. 467-9. 



t Ibid., pp. 461-4. X Ibid-, pp. 1389-91. 



