TYPE MOLLUSC A. 



319 



large pyriform structure, which tapers somewhat to form a 

 vagina opening to the exterior and receives a duct from the 

 receptaculuni semiuis. The vas deferens (vd) shortly after 

 its separation from the hermaphrodite duct dilates into a 

 glandular structure, the prostate gland, from which the nar- 

 row duct passes onward to terminate in an enlarged penis- 

 sheath (pe) which contains the 

 muscular protrusible penis 

 and opens to the exterior 

 quite independent of the 

 opening of the vagina. 



In the majority of the 

 Stylommatophora (Fig. 1-13), 

 however, the two ducts open 

 into a common atrium so that 

 only one genital orifice occurs, 

 as in some of the Opistho- 

 branchs (see p. 312). Other- 

 wise the arrangement is simi- 

 lar to what has been de- 

 scribed for the Basornmato- 

 phora, except that in some 

 forms, as Helix, one or two FIG. 143. REPRODUCTIVE ORGANS OF 

 additional accessory struc- Limax maximus <aftel 

 tures are added. Thus the 

 atrium has communicating 

 with it a sac which contains 

 a sharp calcareous rod, the 

 "dart," which serves as a 

 stimulus during copulation, 

 being plunged into the body 

 of the. other party to the act; 

 and again just at the point where the vas defereus opens 

 into the penis it has communicating with it an elongated 

 tubular structure, the "flagellum," which perhaps furnishes 

 the material of which the capsule of the spermatophores is 

 composed. 



Development and Affinities of the Gasteropods. The devel- 

 opment of the Gasteropods is made interesting on account of 



al = albumiuipavous glaud. 

 hd = hermaphrodite duct. 

 kg hermaphrodite gland. 

 li ligament. 

 od = oviduct. 

 pe = penis-sheath. 

 rs = receptaculum seminis. 

 at = uterus. 

 vd = vas defereus. 

 vs = vesicula semiualis. 



