MOLLirSCA 



253 



have a value in testing the character of the water flowing over 

 them. Still other patches occur about the lips. Otocysts or 

 statocysts (see §111), occur in all the groups. Eyes are usually 

 found and are of various degrees of complexity. They are 

 simplest in the lamellibranchs (Fig. 43), and when found at all 

 in this group may occur in great numbers along the mantle. 



Fig. 114. 



Fig. X14. Diagram of a dissection of the reproductive organs of a snail. a.£., albumen gland ; 

 c.d., common or hermaphrodite duct; e.g., hermaphrodite gland; d.s., dart sac;/t ilagellum; g, genital 

 aperture; m.g., mucous glands; o, oviduct; p, penis; r.s., receptaculum seminis; v.d., vas deferens. 

 The slit from the genital aperture into the oviduct and penis shows the openings of the dart sac. 

 mucous glands, and the receptaculum seminis. (After Pelseneer.) 



Questions on the figure. — By a careful study of the figure and the text, de- 

 termine the functions of the various parts of the system. Does self-fertilization 

 occur in a form like this? Evidences. 



In the gasteropods the eyes are borne on the ends of tentacles 

 and are frequently destroyed by accidents. The animals have 

 the power of regenerating the tentacle, — eye and all. This 

 manifestly is a very useful adaptation. The eyes of fcephalopods 

 are the most perfect single eyes found among the invertebrates. 



