H. Rathke on the Metamorphosis of the Crustacea. 265 



the same form as in these, only their stem had become rela- 

 tively much broader ; but on the two posterior ones, which 

 likewise had become relatively longer, an inner branch had 

 already begun to form, but was not yet articulated. Close 

 behind these organs appeared on the inferior side of the ce- 

 phalothorax two to three pairs of very short but very thick 

 cylindrical and uncinate (hakenformig) much incurved (zu- 

 sammengekrummt) members, of which those of the front pair 

 w r ere slightly swelled at their extremity, and were there pro- 

 vided with a scarcely perceptible incisure ; the others, how- 

 ever, appeared quite simple and obtusely rounded at their 

 extremity. These minute organs were the first indications of 

 true legs. There was no sign of branchiae. The posterior 

 antennas had not changed considerably in form, they also were 

 still but of slight length ; but on the front ones a small rami- 

 fication had already been developed, so that each terminated in 

 two short branches, unequal in length. The snout was about 

 as long as the antennae, of considerable length therefore, and 

 terminated very acutely. The tail had become thicker in com- 

 parison to its length. The lamina of the fan already present 

 in the embryos was of considerable size, but represented an 

 irregular square, which was somewhat broader behind than in 

 front, and had a moderately deep incisure on its hinder margin. 

 Near to the front end of this, a very small lamina, in compa- 

 rison to the above plate, was moveably connected with the 

 sixth joint of the tail on each side ; it was divided by a deep 

 narrow incision into two flaps of unequal size, but not jointed 

 off from each other. These two small plates were the first 

 traces of the lateral laminae of the fan. There were still no 

 false feet on the other joints of the tail. 



In young, which were somewhat above two lines in length, 

 five pairs of true feet already occurred. Although all these 

 were still very small in comparison to the foot -jaws, yet a 

 faintly indicated articulation may be recognized on them, espe- 

 cially on those of the three front pairs ; moreover, the claws 

 (chelae) were already distinctly imprinted on those of the 

 most anterior pair, and these pincers were even larger on the 

 one than on the other. On the other hand, no branchiae were 

 yet decidedly evident. On the fan of the tail the side plates 

 had become larger in proportion to the central plate, and the 

 two unequally sized flaps of each were jointed off (abgeglied- 

 ert). Only slight traces of false feet were perceptible. As to 

 the rest, the organization of these young resembled that of 

 those above-described. 



In still older young, which however were not much longer 

 than the preceding, several organs had already undergone 



