Chilton. — On Astacus fluviatilis and Paranephrops setosus. 155 



carapace and the great claws. In both of these, hut 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 (pi. XXI., fig. 3 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 

 projections were concerned. 



Seta. — There are two kinds of setae found abundantly on various parts 

 of the body. The first (pi. XXL, 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 (pi. XXL, 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 seta3 are found on almost all parts of the body, but they 

 are thickest on the telson, the abdominal appendages, the chelae and the 

 antennae. The jointed setae are found chiefly on the chela? and the an- 

 tennae. On the chelae both kinds are found together forming little clusters 

 each containing about five or six plumose setae and two or three jointed 

 setae. Modified forms of these setae are found in the respiratory organs, in 

 the stomach, and on the antennae, and are described in their proper places. 



Appendages. — The antenmde (pi. 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 sac 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 setae 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 setae, the plumose 

 setae 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). 



