DKECIA — CRYPTOPIIALLIA. 
353 
vas deferens, which may widen into a seminal glandular vesicle or 
prostate in some part of its course. 
The female organs develop) an albumen gland, a glandular sacculate 
oviduct and a more or less definite spermatheca or vesicle to receive 
the fertilizing spermatozoa. All our dioecious Streptoneures, except 
Neritina and Vivipara, are exophalliate, Cydostoma, Bithynia, etc., 
being examples. There is also sometimes a certain degree of external 
sexual dimorphism, the male possessing a slenderer form and a per- 
manently projecting male organ, and the female being larger and 
relatively more turgid. In some genera this dimorphism is variously 
displayed, by Littorina at the mouth of the shell, by Cerithium in the 
operculum, by Nassa in the radula, etc. 
The Cryptophallia (k^wtos, hidden; c^aXAos, penis) are in the 
Dicecia restricted in this country to Neritina Jluviatilis, in which 
the male copulatory organ is stated to be retractile within a penis 
sheath capable of withdrawal 
into the body cavity, as in the 
Pulmonata, although Vivipara 
may also be regarded as 
belonging to this group, as the 
contractile male organ is con- 
cealed within the right teirtacle, 
which is sensibly deformed 
thereby. 
The general character of the 
organization of the dioecious 
Cryptophalliate Gastropods is 
not, however, sensibly diver- 
gent from the usual dioecious 
type, and only differs from the 
Exophallia by the retractibility 
of the male organ, although the 
vas deferens is of an enormous 
length, the prostatic portion of 
its course being combined into 
a large compact mass upon the 
penis sheath, a similar concen- 
tration of the prostate, however, exists in Vivipara, Cydostoma, and 
even in Siicdnea. 
Fig. 6i6. Fig. 647. 
Fig. 616. — Male reproductive organs of Ncri- 
ti7ia Jluviatilis X 4 (after Moquin-Tandon), 
illustrating the Diosciate Cryptophallia. 
t, testis; v.cl. vas deferens or sperm duct with 
enlarged sperm vesicle or epididymis efi. ; pr. 
prostate ; p.s. penis sheath ; 7n.o, male orifice. 
Fig. 617. — Female reproductive organs of Neri- 
tina Jluviatilis {hj, X 4 (after Moquin-Tandon). 
0 . ovary ; ov. oviduct ; alb. gl. albumen gland ; 
sp. spermatheca ; zU. uterus or matrix ; v. vagina ; 
f.o. temale orifice. 
20/3/1900 
X 
