XVI MORPHOLOGY OF GEXITALIA. 



believing that the atrium only is thrust outward. Further investiga- 

 tions of snails during breeding are needed. 



Description of organs: The external opening of the genitalia lie& 

 a short distance behind and below the right (or in sinistral species 

 the left) eye-peduncle. This opens into a short chamber the atrium, 

 (Frontispiece, atr.~), from which the penis (p.) branches toward the 

 digestive tract, and the vagina (vag.') toward the outer side. The 

 penis (p.) is a tube with muscular walls, usually corrugated within, 

 and sometimes having longitudinal fleshy pillars (pilasters, pi. 21 

 fig. 14, 15) adherent along one side to the wall of the cavity. At its 

 distal end the vas deferens (v. f.) enters, its opening being sometimes 

 at the base or summit of a papilla (the penis papilla, pi. 28, fig. 2)^ 

 The penis retractor muscle (r.) is inserted on the penis or its append- 

 ages, and attached distally to the floor of the lung. The vagina(vag.~) 

 branches above into the spermatheca duct (sp. d.) which terminates 

 in the spermatheca (sp.~) ; the other branch (uterus, ut.) becoming en- 

 larged and sacculated. At the apex of the uterus the albumen gland 

 (a. gl.~) supplying the albumen of the eggs, is attached ; from near 

 its base the ovisperm duct springs, and terminates in the hermaphrod- 

 ite gland (h. gl.). 



Besides the above essential organs, the genitalia of many snails 

 are complicated by the presence of various accessory organs. On 

 the male side the penis may bear a gland or sack of unknown func- 

 tion, called the appendix (see pi. 21 fig. 1, 2, 3). This structure may 

 be near its apex, at its base, or even on the atrium. In some groups 

 the vas deferens does not enter the penis directly, but becomes 

 modified into a larger tube the epiphallus (epi.~) which is continued 

 beyond the apex of penis and frequently bears a long blind duct, the 

 flagellum (fl.~). 



The female side in some groups is provided with a muscular sac 

 upon the vagina (or atrium), the dart sack (d. s.), containing a 

 needle or dagger-like calcareous dart (see frontispiece, fig. 5, sec- 

 tion of dart sack, showing dart). Associated with this apparatus are 

 found one or several glands, various in form, the mucus glands (m~ 

 gl.^). In certain forms there is a curved hollow appendage high 

 upon the vagina, which probably serves as a receptacle for sperm- 

 atophores, and has been called the appendicula (see pi. 17, fig. 1).- 

 The duct of the spermatheca in some Helices bears a long blind, 

 tube, the diverticulum (see pi. 63, fig. 8). 



