JOUENAL OF ENTOMOLOGY AND ZOOLOGY 139 



The Alimentary Canal. The mouth opens on the ventral 

 side, as a large, laminated opening covered with ciliated epithe- 

 lium, which leads into a cavity in which the end of the buccal 

 mass projects. This buccal mass consists of two layers of muscle 

 with a food chamber between. The outer layer consists of a 

 heavy mass of circularly disposed fibres, opening anteriorly into 

 the mouth cavity by means of a narrow slit. This outer mass 

 is covered by a regularly ridged cuticle, secreted by a layer of 

 short, columnar cells, which is especially heavy near the free end 

 and becomes thin and flat near the base of the buccal mass. 



Within these circular muscles is a cavity into which projects 

 the muscles over which the radula moves. These consist of two 

 lateral masses, fastened together below by a band of muscle, and 

 aliove by a thin layer which consists mainly of epithelium. Be- 

 tween these two masses is a cavity, which communicates directlj' 

 with the arterial system. The radula is grooved above this 

 cavity so as to dip down into it. Toward the posterior end of 

 the buccal mass sinuses appear between the outer muscles and 

 the epithelium lining the buccal cavity and extend in size, as 

 the buccal food cavity diminishes, so that the posterior part of 

 the muscles of the radula is almost entirely surrounded by 

 sinuses. When this takes place the sinus between the radula 

 muscles communicates with those surrounding them. At the 

 posterior end of the Iniccal mass the ditferent sets of muscles 

 gradually blend together. The gland where the formation of 

 the radula takes place is situated in the continuation of the 

 groove between the muscles over which the radula moves. It 

 is situated at the extreme end of the buccal mass where it pro- 

 jects as a little knob. It is lined with tall slender columnar cells, 

 with a dark-staining granular protoplasm and oval nuclei situ- 

 ated near the center of the cell. At the upper side of the capsule 

 is a mass of unditferentiated tissue from which several layers 

 of large irreg-ular shaped cells branch off. In the space between 

 these two kinds of cells the radula is formed, the teeth probably 

 by the irregular inner cells and the basement membrane by the 

 columnar lining layer. From the mouth the food passes through 

 the cavity between the two sets of muscles, and up over the 



