ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
329 
<y. Gastropoda. 
Anatomy of ‘ Hirondelle * Gastropods.* — M. E. L. Bouvier gives us 
the first of a series of studies on the Gastropoda collected during the 
voyage of the Prince of Monaco. He now deals with the relations of 
the arterial circulatory apparatus to the nervous system. 
In the Prosobranchiata the aorta bifurcates almost immediately after 
leaving the ventricle; its posterior branch plunges into the viscera, 
while the anterior passes under the supra-intestinal branch of the visceral 
commissure ; in the front part of the body it passes above the oesophagus, 
goes through the cerebro-pedal and pallio-pedal collars with it, and then 
divides into several branches unequal in importance. 
In the Pulmonata — e. g. Lymnsea stagnalis — the visceral chain is 
elongated and its ganglia are well separated from one another; after 
reaching the anterior part of the body by passing above the oesophagus 
the anterior aorta passes below the visceral chain, then above the pedal 
commissure, and then divides almost as in the Prosobranchiata. 
Very great differences are exhibited among the different representa- 
tives of the Opisthobranchiata. In Bulla hydatis the anterior aorta runs 
parallel to the right branch of the visceral commissure, and when it has 
reached the level of the pedal ganglion it gives off a cephalic artery, and 
then passes transversely in front of the great anterior pedal commissure. 
About the level of the middle of this commissure it gives off a labial 
and a buccal branch, and, then, on the left forms a cephalic and a recur- 
rent pedal artery. Scaphander lignarius and Philine aperta show much 
the same relations. In Aplysia the anterior aorta passes under the right 
branch of the visceral commissure, above the “ parapedal ” and below 
the pedal and subcerebral commissures. Differences are again found in 
Doris , Polls, and Tritonia. 
Development of Paludina vivipara.f — Herr R. v. Erlanger finds 
that the mesoderm of Paludina vivipara begins to appear soon after the 
formation of the gastrula as a tubular outgrowth of the archenteron. 
This soon becomes constricted off from the gut, and takes on a semilunar 
form, in the cavity of which the gut lies. As the coelomic sac gives rise 
to parietal and visceral lamellae it surrounds the whole of the intestine. 
The mesoderm finally breaks up into the well-known spindle-shaped 
cells which traverse the coelom in a very irregular fashion. 
The pericardium is derived from the coelom, and appears at first 
paired. Soon a small evagination of the wall is seen in the left portion, 
and a little later a somewhat larger one appears in the right. The 
latter forms the permanent kidney, while the former corresponds only 
to a rudimentary left kidney. The pallial cavity appears as a ventral 
ingrowth of the ectoderm just below the pericardium. 
While these processes are going on all the organs found within the 
now formed shell undergo a change in position. Thus the pericardium, 
which was at first ventral and set perpendicularly to the long axis, 
passes altogether to the right half of the body. The heart is formed as 
an invagination of the hinder wall of the pericardium. This invagination 
forms an elongated groove, which soon becomes converted into a tube 
* Bull. Soc. Zool. France, xvi. (1891) pp. 53-6. 
t Zool. Anzeig., xiv. (1891) pp. 63-70. 
