CAMBAKUS. 15 



Peculiarities of the Young Stages of Cambarus. — The young Cambarus, like 

 the young Astaeus, when it loaves the egg is devoid of appendages on the 

 first and sixth abdominal somites. The telson is not divided by a trans- 

 verse suture. I have examined specimens of C. rusticus when but four milli- 

 meters in length, evidently just released from the egg. They have much 

 the same appearance as the embryo of Astaeus fluviabilis just before hatching, 

 as figured by Rathke.* The cephalothorax is very large in proportion to the 

 abdomen, and spherical; the rostrum is bent down bet ween the eyes; the 

 antennas are laid back closely upon the breast, All of the appendages are 

 soft, weak, and flexed beneath the sternum. There is no vestige of a gill on 

 the last thoracic somite any more than in the adult Cambarus. The telson 

 is a thick oval plate, entirely destitute of marginal setse, such as are seen 

 fringing the telson in recently hatched young of Astaeus figured by Huxley 

 on page 220 of " The Crayfish " ; agreeing in this respect with the telson 

 of the embryo of Astaeus as shown in Plate II. fig. 25,. of Rathke's memoir. 

 I have no doubt that the newly hatched young of Astaeus figured by Huxley 

 has undergone one ecdysis since leaving the egg, whereby the embryonic 

 cuticle has been discarded. 



Young specimens of C. Clarkii, seven millimeters long, taken from under 

 the abdomen of the parent, have acquired the general form of the adult. 

 The swimmerets, or posterior abdominal appendages, are well developed. 

 while in the European Astaeus pallipes, ten days old and eleven millimeters 

 in length, these appendages are enclosed within the notched telson. from 

 which they are set free after the second or third moult, judging from speci- 

 mens received from the College tie France. Specimens of C. gracilis, nine 

 millimeters long, and C. Bartonii, ten millimeters long, still under the pro- 

 tection of the parent, have the swimmerets perfectly expanded, and even 

 show the transverse suture of the telson. It seems probable, from a com- 

 parison of these Cambari with the young of European Astaci. I bat the devel- 

 opment of the former goes on more rapidly after leaving the egg than that 

 of the latter. 



It is interesting to observe that in the young C. Clarkii above mentioned 

 the areola is moderately wide in the middle, where it is reduced to a line in 

 the adult ; the lateral spines of the rostrum are well developed, the acumen 

 long and acute. In all the recently hatched Cambari which I have seen, the 

 legs and claws are long and slender compared with the adult. 



* Untersuchungen iber die Bildung und Butwickelung des Flusskrebses, Tab. I Bg. LG, Tab. II. fig. 25. 



