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- 
sammengekriimmt) members, of which those of the front pair 
were 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 branchiz. The posterior 
antennz 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 antennz, 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 laminz 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 
(chelze) 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 branchiz 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 
