Anatomy of the Slug. 335 



lumen. The organ opens anteriorly into the common genital 

 atrium. 



Thu Common yf^iiifal ati^ium (Figs. 2, 5, 6, 7, 8) receives 

 the openings of the penis, the oviduct, and the amatorial organ. 

 It opens to the exterior by the reproductive opening situated 

 just slightly posterior and ventral to the right superior tentacle 

 (Fig. 1). The penis can be protruded through the atrium, and 

 the reproductive opening to the exterior. 



The Alimentapy System. 



The Mouth is situated on the ventral surface, and leads into 

 the buccal cavity. The buccal mass occupies most of the anterior 

 part of the head (Fig. 5). The buccal bulb is lined by an epithe- 

 lium of columnar cells, with very distinct nuclei, the walls are 

 very muscular, the two lateral ones extremely so. The jaw 

 has been described by Mr. Hedley. In section it is seen to con- 

 sist of a layer of chitin, which stains deeply, with a serrated 

 free edge ; the serrations all pointing in the same direction. 

 (Fig. 5.) Under this chitinous layer is a layer of oblong cells 

 with large granular nuclei, the nuclei all being arranged at the 

 ends of the cells away from the chitinous layer. 



The RaduJa (Fig. 6) is so deeply stained in my sections that 

 nothing can be made out of the teeth, but under them is a very 

 clear epithelium, composed of cells with large granular nuclei, 

 and under this a pad of muscle fibres and connective tissue. 

 The radula consists of about ninety-six rows of very fine teeth. 

 The shapes of these teeth were distinguished from preparations 

 of the radula both unstained and stained with picro-carmine. 



The Rachidian (Fig. 3) is tricuspid, the three cusps twisting 

 around each other in such a manner that it is only by careful 

 focussing that the shape can be seen. The base is roughly 

 conoid. 



The shapes of the laterals and marginals which gradually 

 merge into one another can be best understood by reference to 

 the figure (Fig. 3), which represents some of them from a 

 lateral view, taken from a teased radula and arranged as far as 

 possible in order. 



