Cumton.—On Astacus fluviatilis and Paranephrops setosus. 168 
Olfactory organs.—These are borne on the exopodite of the antennule. 
The various joints in the flagellum differ in shape from those of Astacus, 
for the distal end of each is considerably enlarged; this enlargement is 
chiefly on the under side, for, while the upper edge is nearly straight, the 
under edge curves so as to form a rounded protuberance towards the distal 
end (pl. XXL, fig. 1). On these protuberances are situated the tufts of 
olfactory sete (c), thus there is only one tuft of olfactory sete on each 
joint, wbile in Astacus there are two on each joint. Each tuft arises 
from a slight cavity in the joint and consists of usually five or six olfactory 
setze. 
The olfactory sete are similar in shape to those of Astacus. Hach con- 
sists of two parts (pl. XXI., fig. 2), which at first sight appear to be divided 
by a joint, but on more careful observation it appears that this is not really 
$0, but that the walls of the two parts are continuous, and that the appear- 
ance of a joint is caused by the basal part being filled with opaque granular 
matter while the distal part is clear and transparent. This opaque gran- 
ular matter extends up the sides further than it does in the middle of the 
seta. 
Reproductive organs.—Male (pl. XX., fig. 7). The testes (t) consist of 
two long tubes united towards their anterior ends by a transverse portion or 
commissure. The two parts in front of this commissure lie between the 
heart and the posterior portion of the stomach, and are somewhat directed 
upwards towards the dorsal surface of the body. Immediately in front of 
the commissure they become considerably narrower. The portions of the 
tubes behind the commissures are narrow at first but they soon widen and 
then soon contract again at the origin of the vasa deferentia. After this they 
again widen out and at their posterior ends are more closely approximated. 
Thus a little behind the commissure a considerable space is left between the 
two tubes, and in this space the heart rests. The vas deferens (vd) arises 
as a very fine tube. The first part differs from the remainder in being 
smaller and less boldly curved. The remainder is exceedingly convoluted 
and increases only very slightly in size until it comes to the portion which 
proceeds directly downwards to the aperture on the bases of the last pair of 
ambulatory legs. This (a) is enormously expanded and is not quite 
cylindrical, being somewhat laterally compressed. In the figure the con- 
volutions have been separated. I have not been able to observe the 
spermatozoa, but I have seen in some specimens the other substance 
which Professor Huxley mentions as filling the vasa deferentia together 
with the spermatozoa. As in Astacus it was of a viscid material and 
gave “the secretion of the testis the form and consistency of threads of 
vermicelli,” 
