409 
of Gasteropodous Mollusca. 
of digestion, and is highly complicated and of great extent, filling 
by far the largest portion of the body. Each individual possesses 
both male and female organs, as well as the additional apparatus 
of a spermatheca, as observed in the Nudibranchs. The external 
orifices are placed on the right side of the body and are three in 
number ; two immediately below the eye, and one nearly half-way 
along the body. Of the two anterior orifices, the one in front 
h that of the male intromittent organ (PL XX. fig. 4 a), and the 
other, which is close behind it, is that for the passage of the ova 
(/) ; the third orifice (m) is in communication with the sperma- 
theca, and is that by which impregnation is effected. Of the 
position and nature of these orifices there can be no doubt, for 
we have had frequent opportunities of observing the animals 
during coitus, and have also seen them when spawning. The 
male intromittent organ lies doubled upon itself immediately 
' within the orifice, and when partially exserted (fig. 4 a) is of a 
subconic form, but is capable of much elongation and attenua- 
tion. The point (figs. 4 & 5 is furnished with a minute curved 
crystalline spur-like process, which is perforated (fig. 6 a) . The 
base of this process is united to a tube (figs. 4c & 5 c), which, pass- 
ing through the axis of the penis, runs a short way backwards 
and is joined by the oviduct aty, immediately after it is united to 
the duct of the testis at g, and then terminates in an elliptical 
bulb {p) at the end of the copulatory passage, just^where it receives 
the duct of the spermatheca (r). Near to the point where the 
oviduct joins this tube, it is attached to what occasionally assumes 
the appearance, in the compressor, of two elongated glands (m) 
with undulated walls, but which is very possibly a portion of the 
large mucous gland belonging to the female parts, afterwards to 
be more fully described. In tracing the male organs backwards, 
it is seen that the duct of the testis, after its union with the 
tube of the penis, runs for a short way parallel to the copulatory 
channel, as will be by and by more particularly mentioned ; and 
after communicating with it at /, soon reaches the median line of 
the body, about midway between the head and the tail. The 
duct of the testis then suddenly dilates, and, almost directly 
afterwards, divides into two branches, one going to each side of 
the body [d d ) ; here these branches again divide into two nearly 
equal portions, one of which goes towards the head, the other 
towards the tail ; these portions divide and subdivide two or three 
times, the extremities ending in blind sacs. This multiple organ, 
there can be no doubt, is the testis, though we have no direct evi- 
dence in proof of this. Its anatomical relationship, however, 
appears sufficient to warrant this opinion. 
The ovarium (// h h), like the testis, is also divided into two 
parts ; one, much the larger [h h), occupies the posterior portion 
