REPRODUCTIVE ORGANS— SARCOBELUM. 
365 
typical form take no part in the true coupling, serving only as their 
name implies to provoke that act. 
Excitatory functions are not, however, a trait restricted to either 
sex, as stimulatory adj uucts to both the male and female organs have 
been demonstrated to exist, and it is probable that most mollusks 
are provided with special stimulatory organs or possess some other 
means of allurement or attraction to sexual union. 
According to their character the excitatory organs may be grouped 
under the two heads, Sarcobela and Gypsobela. 
The Sarcobelum (a-apyo, flesh; /5eA.os, an arrow) or e.xcitatory organ, 
the “reizkorper” of the Germans, “organ 
excitateur” of the French, is usually a 
soft and fleshy ling inform eversible pro- 
cess, erectile by blood pressure, and 
occasionally furnished with a harder cal- 
careous point with which each animal 
strokes, pats, and caresses its prospec- 
tive partner during their amorous pre- 
ludes. This organ is usually located 
within the genital passage, near the 
outlet, and may be cleft at the base for the passage of the copula- 
tory organs. 
Unlike the Gypsobelum, which is more particularly an adjunct to 
the female system, the Sarcobelum is more especially, though not ex- 
clusively, a masculine excitatory organ, and is usually present in the 
form of an erectile muscular 
appendage within the penis 
sheath, as exemplified in 
Agi-iolimax agrestis and 
other species, but similar 
alluring developments exist within the atrium of other species, occu- 
pying an intermediate position between the two groups of organs in 
the hermaphrodite species and not strictly supplementary to the 
organs of either sex, or these stimulating appliances may, as in 
Amalia, be slightly within the vagina or other feminine duct, and 
really appertain to the female system. 
In the Dioecious Viviparidw we find a probable prototype of the 
Egersidium in the erectile fleshy appendage upon the inner walls of 
the vaginal tube, which may be regarded as a primitive Clitoris or 
Fig. 667. — Spermatheca duct of 
Zua lubrzca{lsl\i\\.\ X 30, laid open 
to show position and character of the 
sarcobelum or excitatory organ (after 
Ihering). 
Fig. 668. — Ag^olzmax agrestis with its sarco- 
belous excitatory organ protruding. 
