The anatomy of Lottia gigantea Gray. 



9 



rather smaller than those on the lips, and are disposed in irregular 

 transverse rows. They are larger on the posterior half of the organ 

 and extend forward nearly to the tip, and on either side, to the 

 longitudinal groove. They have been noted and figured by Thiele 

 in Acmaea digitalis, A. virginea and A. viridula. The interior of the 

 organ is filled with muscles except a large central space where the 

 blood enters. This supply of blood is derived directly from the sub- 

 lingual artery, a ventral branch of the cephalic, and both observation 

 and experiment show that the organ is distended by the blood. It is 

 retracted by special muscles lying under the radula protractors. The 

 nerve supply, which is rather rich, springs from the subradular ganglia. 

 These ganglia are situated on the lower side of the subradular pocket 



Fig. E. a) the sublingual organ and one palp from Fig. D enlarged, c cuticle, 

 Lat. P lateral pouch, M. C mucous cells ; b) cross section through rectum near left ureter 

 to show folds in walls. 



at its far end, and are connected by slender nerves with the lingual 

 ganglia. Nerves are given off which pass along the dorsal wall of the 

 subradular pocket and spread out in a network under the epithelium 

 of the sublingual organ. One is not prepared to say definitely whether 

 or not the sublingual organ is homologous with the subradular organ 

 of the chitons but it is certainly a significant fact that the sublingual 

 organ is innervated by the subradular ganglia, which I believe are 

 homologous with those of the chitons. These ganglia will be treated 

 more fully under the nervous system. 



Extending backward under the odontophore and sublingual organ 

 is the subradular pouch (Fig. 4). Along the middle of this is a trough- 



