316 MR. F. F, LAIDLAW ON THE [ Apr. 21, 
a loss to explain satisfactorily. In the first place, the testes and 
ovaries are very immature, and apparently only the terminal parts 
of the genital ducts are developed. On the other hand, there is, 
immediately over the penis, a large mass of mature spermatozoa 
lying in a chamber the character of which cannot be determined 
from my specimens, since it appears in places to have indications of 
a proper lining-epithelium of its own, and again in places seems to 
be merely a gap in the parenchymatous tissue. There are very 
faint indications of a duct running from this chamber down in 
the direction of the penis, but this duct cannot be traced far. 
Woodworth [16] suggests in connection with the specimens of 
Diposthus described by him, that they were in a late stage of 
sexual activity, and that in consequence of this the sexual organs 
were in a reduced condition. Possibly in my specimens of 
Asthenoceros a similar state of affairs occurs, but, as I have 
already stated, testes and ovaries in a very immature state are 
present. There is also a possibility that the ripe spermatozoa 
may be derived from another individual by hypodermic injection ; 
but I do not think this is the case—firstly, because the penis is 
not armed with a stylet; and, secondly, because the spermatozoa 
lie over the penis, and because, as already stated, there are traces 
of a duct running towards the penis from the chamber in which 
they lhe. 
The terminal parts of the male apparatus histologically resemble 
those of Diposthus. The prostate and penis are separated into 
two distinct organs, “both of which are doubtless intromittent,” 
both opening by a single gonopore. The prostate lies immediately 
in front, the penis directly over the aperture. It is rather 
feebly supplied with muscle-fibres, and the secretory cells le in 
the middle of the organ, but there is no lumen apparent 
(cf. Diposthus corallicola). 
The penis ismuch more muscular, and on the outer side has a 
very definite series of circular and longitudinal fibres. Nuclei in 
it too are much more numerous (Pl. XXIII. fig. 7). 
In connection with the female organs there are traces of two 
pairs of uterine vesicles. The uteri are very small and difficult to 
distinguish from the surrounding tissue, and the ducts running 
to them are merely solid rods of cells of an embryonic appearance. 
The uteri open into the hinder end of the vagina. The antrum 
is deep, and widens at its upper end where it receives the secretion 
of the shell-glands. 
The body epithelium is very densely crowded with small 
rhabdites, and on the dorsal side especially with pseudorhabdites. 
Scattered through the parenchyma, more particularly in the region 
of the sucker, are numbers of small rounded darkly-staining cells 
the nature of which is doubtful. The ventral surface of the body 
projects immediately behind the pharynx into a prominent median 
ridge which carries the gonopores and the sucker ; behind the 
sucker the ridge disappears. 
I have given as complete an account as possible of the cha- 
