TRANSVERSE SECTIONS 97 



After a couple of days transfer it to spirit and keep it till 

 wanted. 



To make the sections, remove both valves of the shell care- 

 fully ; place the animal on a board, and cut it with a razor 

 into a series of transverse slices about a quarter of an inch 

 thick ; arrange the sections in order in a dissecting dish under 

 water ; examine and draw them. 



The most instructive sections are those passing, (1) through 

 the renal and reproductive apertures ; (2) through the middle 

 of the ventricle ; (3) through the posterior adductor. The 

 chief features of these sections are as follows. 



A. Transverse Section through the Renal and Reproductive 

 Apertures. 



The section passes through the widest part of the body, a 

 little way behind the umbo. 



1. The mantle-folds arise very close to the dorsal surface, 



one on each side of the pericardial cavity. The 

 folded margin which secretes the shell should be 

 noticed. 



2. The visceral mass is large and laterally compressed, 



and lies in the middle of the section between the two 

 mantle-lobes. The chief part of its substance is 

 made up of the lobes of the generative gland. The 

 ventral edge of the visceral mass is produced into the 

 wedge-shaped muscular foot. 



3. The alimentary canal. The coils of the intestine are 



seen in the visceral mass, imbedded in the genera- 

 tive gland, and cut across about half a dozen times. 

 Lying in the pericardial cavity in the median line 

 immediately beneath the dorsal surface is the rectum, 

 in which the typhlosole or fold of its ventral surface 

 is well seen. 



4. The gills lie in the dorsal half of the mantle -cavity, 



between the visceral mass and the mantle. The 

 attachments of their lamellae to the body-wall are 

 well seen. The inner lamella of each inner gill is 

 attached to the base of the visceral mass. 



