of Gasteropodous Mollusca. 411 
a brownish yellow colour. It lies a little behind the buccal mass, 
near the median line of the body. From its right side issues a 
small duct (r), which, turning backwards, communicates with the 
bulb (p), or dilated portion of the copulatory passage, at the 
point where it receives the tube of the penis. From thence the 
copulatory passage or channel {o) leads backwards, and for a 
short way runs parallel to the duct of the testis, to which it is 
closely adherent ; it soon contracts and turns to the right side. 
At the point where the contraction takes place it communicates 
at /with the duct of the testis; afterwards the walls of the chan- 
nel continue parallel until it approaches the external orifice, when 
it suddenly expands into a sort of shallow pouch {n). During 
copulation, the intromittent organ, entering at this orifice, will 
pass along the channel just described, probably as far as the bulb, 
or dilated portion, in connexion with the short duct of the sper- 
matheca ; from thence the seminal fluid will readily reach that 
vesicle, to be there retained until required for the fertilization of 
the ova. How this takes place will be seen if we trace the eggs 
from the ovary to the external outlet. 
The eggs pass from the ovigerous sacs by the small ducts be- 
fore described, and, reaching the central duct, find their way at 
once into the dilated portion {i) of the common oviduct ; and 
there, probably, are advanced another step towards maturity : 
they then pass along the constricted part of the oviduct, and 
reach the tube of the penis near its junction with the bulb of the 
copulatory passage, when they will be within the influence of the 
fluid stored up in the spermatheca, and also of that of the testis 
of the same individual. The bulb (p), or dilated portion of the 
channel leading to the spermatheca, may be probably a sort of 
reservoir for the retention of the fertilizing fluid secreted by the 
testis of the same individual. If so, this fluid may be supposed 
to pass from the duct of the testis at the point (/) where it com- 
municates with the swelled portion of the channel, and it may 
be here that the eggs are fertilized. During coitus the seminal 
fluid will pass directly onwards through the duct of the testis to 
the tube of the penis. And thus, perhaps, we arrive at a correct 
understanding of the function of those two points of union. The 
eggs, after being thus fertilized, pass downwards into the chan- 
nel of the great mucous gland (/:), and then become enveloped in 
their final covering previous to expulsion through the opening 
(/) at the base of the penis. 
It would appear, from the diagram of Chalidis caerulea given 
by M. de Quatrefages, that he has confounded the ovary with 
the testicle, and that which is called the testicle is probably a 
portion of the great mucous gland. The salivary gland has the 
