204 SUMMARY OF CURRENT RESEARCHES RELATING TO 



tho Mollusoa to the bilateral animals; after discussing the develop- 

 mental history of tho nervous system, the differentiation of the mesoderm, 

 the formation of the ccelom, and tho development of the heart and 

 pericardium, he thinks sufficient evidence is afforded of the relationship 

 of the Mollusca to Annelids ; but this raises the question of segmenta- 

 tion, and we know that the postoral part of molluscs is not segmented. 

 To explain this, it is necessary to suppose that the deviations from the 

 ancestral form common to the two groups began at a larval stage, and 

 have since been gradually impressed on the organization of the animal. 



Anatomy and Affinities of Ampullaria.* — M. E. L. Bouvier adds 

 to our knowledge of this amphibious mollusc, the nervous system of 

 which he has already described. It has both a monopectinate gill like 

 all the Monotocardia, and a false bipectinate gill like the most highly 

 organized of that group. The false gill lies to the left of the lung and 

 the true gill to the right ; both are innervated by the left supra- 

 intestinal branch of the visceral commissure, and so correspond to the 

 same organs on the left side of other Monotocardia. The left kidney is 

 a large chamber with the floor alone glandular ; the spiral portion of the 

 intestine, the ovary and albumen-gland of the female, and the seminal 

 reservoirs of the male project on to this floor, and appear to be situated in 

 the cavity of the chamber. The cavity of the left kidney communicates 

 anteriorly and on the right with that of the right kidney ; the latter is 

 lined by lamellas arranged around a dorsal and a ventral vein. The 

 renal products make their way to the exterior by a cleft in the walls of 

 the right kidney ; they pass into a conical canal which ends at a groove 

 placed between the recto-genital mass and a dorsal lamellar pad. As in 

 Haliotis, the venous blood from the left kidney goes directly to the 

 heart, while that from the right kidney first passes to the gills. 



The anterior part of the digestive tracts recalls by its relations to 

 the nervous system and the salivary gland the diotocardate Proso- 

 branchs ; there is a gastric cascum, and the intestine is coiled spirally 

 in the cavity of the left kidney. As has long been known, the circula- 

 tory system is remarkable for the presence of an arterial ampulla which 

 is lodged in the pericardium and situated at the base of the anterior 

 aorta. The posterior aorta is replaced by five arteries, one of which 

 branches on the wall of the intestinal spire. 



Notwithstanding certain anatomical resemblances to the Naticida?. 

 and the diotocardate Prosobranchs, the Arnpullarige appear to be closely 

 allied to the Paludinidee, and especially to the Cyclophoridse ; but a 

 little more than either of these they tend to approach the higher 

 Prosobranchs. 



Development of Heart of Pulmonate Mollusca.f — Mr. W. Schim- 

 kewitsch has a note on the investigations into the development of the 

 heart of pulmonate molluscs lately made by M. Schaalfeew. The 

 latter gentleman has studied Limax agrestis, and he finds that the 

 pericardium first appears as a compact accumulation of mesodermic 

 cells in which the pericardiac cavity is, later on, formed by delamination. 

 The heart arises as a thickening of the inferior wall of the pericardiac 

 vesicle. The dorsal wall gives rise to a fold which divides the peri- 

 cardiac cavity into two parts ; of these the right forms the glandular 

 part of the organ of Bojanus, while the excretory duct is formed from 



* Comptes Eendus, cvi. (1888) pp. 370-2. t Zool. Anzeig., xi. (18S8) pp. 64-6. 



