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 DE G-EER, are so unlike in form to the parent animal 

 that 0. F. MUELLER formed distinct genera of them, Nauplius and 

 Amymone; flat, oval, without tail, with four or six feet very thick, 

 and radiating from the body 1 . Young individuals of Ergasilus, 

 AchthereSj Lernceacera, present similar forms with four or six feet, 

 according to the observations of NORDMANN 2 . 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 larvae 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 antennas 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 GOODSIR) , 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 



DACE'S Physiologic, n. s. 248 276, and his Commentatio de Animalium Crustaceorum, 

 generatione. Regiomonti, 1844, 4to. 



1 DE GEEK Me moires pour I' Hist, des Ins. vn. pp. 489 491, PI. 30, figs. 6, 7, 8; 

 JURINE Hist, des MonocL; RAMDOHR Betir. zur Naturyesch. einiger deutscken Monocu- 

 lusarten, s. 5, 6, &c. 



2 Mikrogr. Bdtrdge, n. Tab. n. fig. 7, Tab. iv. fig. 7, &c. 



