CRUSTACEANS. 613 
In very many crustaceans extremely remarkable metamorphoses 
have been observed, which, however, are confined to the first period 
of life; long before they are full-grown, they have attained their 
permanent form, and after that only undergo repeated moultings. 
The young of Cyclops, already observed by LEEUWENHOECK and 
afterwards by Dr Grrr, are so unlike in form to the parent animal 
that O. F. Murs.uer formed distinct genera of them, Nauplius and 
Amymone ; flat, oval, without tail, with four or six feet very thick, 
and radiating from the body*. Young individuals of Hrgasilus, 
Achtheres, Lerneocera, present similar forms with four or six feet, 
according to the observations of NorpbMANN?. Also the Cirripedia 
present themselves at first under such a form as this, with which, 
however, that of the young of Apus agrees still nearer, that has no 
abdominal feet, and possesses two pairs of feet, of which the second 
extends behind the body. [But the larvee of cirripeds pass through 
three different stages. In the first the larva, whilst yet in the sac 
of the parent, is nearly globular, with lateral horns. Posteriorly, on 
the sternal surface, are two other minute horns pointing backwards. 
These horns are cases in which the antenne are being developed. 
There are three pairs of feet close together in a longitudinal direc- 
tion, some way apart in a transverse. The first pair has always a 
single ramus or filament, not articulate in some genera, multi- 
articulate in others. The abdomen, a little beyond the end of the 
carapace, terminates in a slightly upturned tail. The mouth is 
undergoing development on a prominence between the bases of the 
feet. ‘Towards the second stage, the most conspicuous character is 
the great elongation of the posterior point of the carapace, whilst the 
abdomen is prolonged, and has two very long spear-like processes 
on its outside (Balanus Goopsir), or terminates in a single tapering 
spinose projection (Lepas THompson). In the second stage, the 
body is prolonged behind the three pairs of limbs and ends in a 
blunt point, in which, probably, the three posterior pairs of feet, 
and the abdomen of the larva in the last stage, are developed. The 
DACH’S Physiologie, 11. s. 248—276, and his Commentatio de Animalium Crustaccorum 
generatione. Regiomonti, 1844, 4to. 
1 De GEER Mémoires pour Hist. des Ins. vit. pp. 489—491, Pl. 30, figs. 6, 7, 8; 
JuRINE J/ist. des Monocl.; Rampour Beitr. zur Naturgesch. einiger deutschen Monocu- 
lusarten, 8. 5, 6, &e. 
2 Mikrogr. Beitrdge, 1. Tab. 11. fig. 7, Tab. Iv. fig. 7, &e. 
