426 EPIZOA. 



velopment is accomplished : this arrangement we have already had an 

 opportunity of examining in the Entomostracous Crustaceans. 



(1097.) The internal ovaria (fig. 221, /), when distended with ova, 

 occupy a great part of the cavity of the abdomen, and present a racemose 

 appearance ; but when empty, as represented upon the opposite side of 

 the same figure (e), each is found to be a simple blind canal with saccu- 

 lated walls, opening externally by an orifice (g g) through which the ova 

 are expelled into the egg-sacs, where their development is completed. 



(1098.) It would seem that, even when the eggs are hatched, the 

 excluded young are far from having attained their perfect or adult form, 

 but undergo at least two preparatory changes or metamorphoses, during 

 which they become possessed of external organs so totally different from 

 those they were furnished with on leaving the egg, that it would be 

 difficult to imagine them to be merely different states of existence 

 through which the same animal passes. 



(1099.) On first quitting the egg, the young Acfitheres is, in fact, by 

 no means adapted to the parasitical life to which it is subsequently 

 destined possessing no organs of prehension like those of the adult, 

 but merely two pairs of swimming-feet, each armed with a brush of 

 minute hairs, and calculated to propel it through the water. Before, 

 however, the first change is effected, another set of feet may be per- 

 ceived through the transparent external covering, encased, as it were, 

 in the first ; when these are completely formed, the original skin falls 

 off, displaying, in addition to the two new pairs of swimming-feet, three 

 pairs adapted to prehension ; and it is only when the second set of feet 

 is thrown off in a similar manner that the animal assumes its perfect or 

 mature form. 



(1100.) In Lamproglena pulchella we have a still more decided 

 exemplification of the Crustacean type of structure, and the rudimentary 

 feet, arranged in symmetrical pairs, are as numerous as the segments of 

 the body. The limbs, however, are as yet only adapted to secure a firm 

 hold upon the structures whereunto this parasite attaches itself, namely 

 the gills of the Chub (Cyprinus Jeses), in which situation it is most 

 usually found. The two anterior pairs (fig. 222, 6, c) are far more largely 

 developed than those which are placed upon the posterior parts of the 

 animal, and are apparently strengthened by a cruciform cartilaginous 

 framework, seen through the transparent integument. The first pair 

 of these holding-feet consist of two robust and powerful hooks, termi- 

 nated by simple horny points ; whilst the second, which are likewise 

 unciform, terminate in trifid prongs, and are evidently equally adapted 

 to prehension. The four pairs of members that succeed to these are 

 mere rudiments, and can be of little service as organs of attachment ; 

 but, to make up for their imperfection, we find at the posterior extre- 

 mity of the body, between the orifices of the ovaria (y), a pair of carti- 

 laginous suckers, well calculated to fix this part of the animal. 



