2 4 8 



ZOOLOGY. 



them. Still other patches occur about the lips. Otocysts (see 

 1 08) occur in all the groups. Eyes are usually found and are 

 of various degrees of complexity. They are simplest in the 

 lamellibranchs (Fig. 41), and when found at all in this group 

 may occur in great numbers along the mantle edge. 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 mani- 

 festly is a very useful adaptation. The eyes of cephalopods 

 are the most perfect single eyes found among the invertebrates. 



FIG. 112. 



FIG. 112. Diagram of a dissection of the reproductive organs of a snail, a.g., albu- 

 men gland; c.d., common or hermaphrodite duct; e.g., hermaphrodite gland; d.s., dart 

 sac; f, flagellum; g, genital aperture; tn.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 recep- 

 taculum seminis. (After Pelseneer.) 



Questions on the figure. By a careful study of the figure and the 

 text, determine the functions of the various parts of the system. Does self- 

 fertilization occur in a form like this ? Evidences. 



