vra PRACTICAL DIRECTIONS 417 



animal in water under a low power after removing the shell 

 in order to see the two globular statocysts, each lined by 

 epithelial cells and containing a lithite, which is in constant, 

 trembling motion. 



VII. The alimentary organs are embedded in solid tissue 

 in the visceral mass, the hinder part of the intestine or 

 rectum alone being surrounded by a ccelomic cavity (peri- 

 cardium). The anus has already been seen. 



1. Remove the animal entirely from the shell, and pin 

 down through the adductor muscles and foot under water. 

 Dissect away the epiderm to the left side of and above the 

 stomach (if this has not already been done), and note the 

 brown digestive gland in the anterior dorsal part of the 

 visceral mass. Then insert a seeker into the stomach through 

 the mouth, to act as a guide, and slit up the short gullet 

 and stomach. Note the ducts of the digestive gland opening 

 into the stomach. 



2. In the same manner slit up the whole intestine, either 

 from the stomach backwards or from the rectum forwards, 

 using the seeker as a guide the whole way, and first examin- 

 ing Fig. 101 to see the direction which the coils take. Note 

 the ventral typhlosole in the rectum, beginning at the last 

 coil. Sketch. 



VIII. i. The gonads appear very similar in both sexes, 

 and fill up a large part of the visceral mass between the 

 coils of the intestine : their ducts open at the genital aper- 

 tures (11, 6). 



2. Tease up a bit of the ovary or spermary in salt-solution, 

 stain with magenta, and examine. 



C. Transverse Sections (Fig. 103). 



With a sharp scalpel or razor cut a specimen hardened in 

 spirit or formaline into transverse sections about J inch 

 thick, passing obliquely through 



i. The anterior part of the pericardial cavity, visceral 

 mass, and foot. Note the relations of the mantle-folds, the 

 gonads, the enteric canal (including the rectum with its 

 typhlosole), the gills and supra-branchial canals, the anterior 

 aorta and vena cava, and the kidneys and bladders. 



2. The ventricle, auricles, and hinder part of the visceral 

 mass. Note the relations of the mantle-folds, enteric canal, 

 gills, supra-branchial canals, vena cava, kidneys, and bladders. 



3. The posterior adductor muscle, hinder part of gills, 

 and rectum. Note the relations of the various parts. 

 Sketch the three sections. 



