Cumron.—On Astacus fluviatilis and Paranephrops setosus. 155 
carapace and the great claws. In both of these, but more especially in the 
latter, the integument is very thick and hard and is beset with many strong 
sharp spines. 
By making sections of parts of the integument it was found to be much 
the same as that of Astacus figured on page 191 of “ The Crayfish.” It 
showed the epiostracum (pl. XXL, fig. 8 a), the ectostracum (b), and the 
endostracum (c), the last being much thicker than the other two together. 
In the inner part of the ectostracum there were numerous rectangular pro- 
jections extending from the endostracum about half-way into the ectostracum, 
but these were very irregular, no two sections being alike as far as these 
—— were concerned. 
ete.—There are two kinds of sete found abundantly on various parts 
of = body. The first (pl. XXI., fig. 8) consists of a central stem which 
bears numerous filaments on it, so that it is densely plumose. The stem is 
all in one piece and is not jointed. In the other kind (pl. XXI., fig. 7) the 
stem has a kind of joint about the middle. The basal half is quite naked 
but the terminal half is minutely serrate towards the end, which is usually 
slightly curved. Both kinds are lodged in a sort of socket in the integu- 
ment at their base. 
The plumose sete are found on almost all parts of the body, but they 
are thickest on the telson, the abdominal appendages, the chele and the 
antenne. The jointed sete are found chiefly on the chele and the an- 
tenne. On the chele both kinds are found together forming little clusters 
each containing about five or six plumose sete and two or three jointed 
sete. Modified forms of these set; are found in the respiratory organs, in 
the stomach, and on the antenns, and are described in their proper places. 
Appendages.—The antennule (pl. XIX., fig. 1) has the peduncle formed 
of three joints. The first or basal joint is somewhat longer than the other 
two together and is broader at its base than at its distal end. On the 
inner side towards the distal end there is a single, strong, sharp spine. 
The outer edge is thickly beset with plumose cilia. The aperture of the 
auditory sae is on the upper side of this basal joint. The next two joints 
are slightly narrower than the first, but they are much broader in com- 
parison than the two corresponding joints in Astacus. Both bear numerous 
plumose sete on either side. The third joint supports the two flagella 
which represent the exopodite and endopodite. The outer one, exopodite 
(ex), is larger and longer than the inner one, endopodite (en). In both of 
the flagella each joint bears some of the two kinds of sete, the plumose 
sete being the more numerous on each joint. In addition to these most of 
the joints of the endopodite bear a tuft of olfactory filaments (see olfactory 
organs). 
