The anatomy of Lottia gigantea Gray. 7 



when seen from the outside, resembles an incipient lower "jaw". As 

 shown in Figs. D and E the jaw is .secreted by a fold of the same 

 epithelium which lines the remainder of the buccal cavity, and in fact 

 the inner surface of the jaw is in direct continuation with the cuticle 

 which covers to a greater or less thickness all the interior of the 

 mouth. The upper and outer corner of the jaw is thin and rounded 

 (Fig. 10) and rests over the knob of each anterior lateral cartilage 

 of the buccal mass. It has no connection with this cartilage, but is 

 held in place by a heavy muscle (15 Figs. 4, 5, 9, 10) which passes down- 

 ward under the cartilages, and partly attaches to their under surfaces, 

 partly continues with the same muscle of the other side. Hence this 

 muscle is a sort of anchor which tightly binds the jaw against the anterior 

 lateral cartilages. Muscle 15 is also attached to these cartilages, and 

 serves as a support or binder for them. Another strong muscle 

 (16 Figs. 5 and 9) originates from the hinder end of the main carti- 

 lages and attaches on each side of the jaw below 15. Both 19 and 

 25 are retractors attached to the edge of the jaw and they serve to 

 anchor it in place, as do also the small muscles (20 Fig. 3). I am 

 unable to judge just how much these muscles, 19 and 25, are able to 

 retract the jaw. Undoubtedly 15 holds the structure firm whenever 

 it is used for scraping, if such is its use. 



In this connection the buccal cartilages may be mentioned. Their 

 general appearance when viewed from above can be better seen from 

 Fig. 13 than described. The two main cartilages end posteriorly in ven- 

 trally directed divergent prolongations, which serve for the attachment 

 of the heavy muscles working the radula. Anteriorly the blunt 

 terminations are closely apposed and form the support of the rasp or 

 odontophore. The two lateral cartilages are attached to the median 

 ones only by dorsal and ventral muscles which hold them firmly in 

 place. The median cartilages are bound together by loose tissue of 

 the same nature as that composing the cartilages themselves, though 

 much less firm. Small transverse muscles also aid in this binding. 

 The cells composing the cartilage tissue are large with heavy walls 

 and prominent nuclei. In section no cell substance is seen, only the 

 heavy meshwork formed by the walls. 



The palps are two thick folds of the lateral walls of the buccal 

 cavity, extending from each side toward the center, where they meet ? 

 and when the animal is not feeding, cover the radula and sublingual 

 organ (Pp Figs. 2, 4, 5, 9, 11 etc.). Their dorsal and ventral limits 

 are well shown in Figs. 2 and 4. The position of the palps, sub- 



