REPRODUCTIVE ORGANS — FLAGELLUM, ETC. 
361 
the integument. The primitive external spermatic groove present in 
the ancestors of the Pulmonates, and still persisting in some Opistho- 
hranchs, has left indication of its former presence and external position 
in the lateral or genital groove connecting the pallial opening with the 
reproductive orifice which is still found in so many species. 
The Flagellum {flagellum, a whip-lash) is the blind diverticulum 
often found in highly organized Gastropods as a prolongation of the 
epiphallus or of the distal end of the penis-sheath, wherein is secreted 
Fig. 658. — Male reproductive system of 
Bithynia tentaculata (L.), X 6, showing the 
semi-independent flagellum. 
t. testis ; v.d. vas deferens terminating at 
the apex of penis \fl. flagellum, opening in a 
separate but subsidiary prominence thereon. 
a sheath or case for the safer transfer of the seminal element to the 
partner. It is very variously shaped, externally and internally, and 
the spermatophore moulded within it is an exact reproduction or cast 
of the shape and denticulations of the interior of the coecum. 
In Bithynia and certain species of Streptoneura, as well as in 
Ancyliis, the flagellum opens to the exterior more or less indepen- 
dently of the penial orifice of the sperm duct, the orifice of the 
flagellum in Bithynia being upon a subsidiary but distinct bilobation 
of the penis ; an intermediate but interesting modification of this 
form of flagellum is found in Buli- 
miniis and Pupa, in which the flagel- 
lum does not form a continuation of 
the distal end of the penis-sheath as in 
Helix, etc., but opens into the common 
vestibule or into the lower part of the 
penis sheath, and it would appear not 
improbable that the appendix to the 
penis-sheath of certain Gastropods is 
homologous with this organ. 
The Epiphallus (stti, upon ; <^aAAos, 
penis) or Patronenstrecke, is merely an 
enlargement of the anterior end of the 
vas deferens, and includes the tract 
between the outlet of the vas deferens 
and penis, and has not usually a retractor muscle, nor is it evertible 
Fig. 659. — Reproductive organs of 
Bulimmus 7iiontanus (Drap.), X 3, 
showing the epiphallus and also the 
flagellum subsidiary to but proximally 
connected with the penis. 
albumen gland ; ot, ovotestis 
h.d. hermaphrodite duct; ov, oviduct; 
v, vagina ; JJ. flagellum ; v.d. vas defe- 
rens ; ep. epiphallus ; p.s. penis sheath ; 
r. retractor; sp. spermathecaand branch. 
