422 



EPIZOA. 



obtained, and where, at the same time, the water in which they are im- 

 mersed is perpetually renewed for the purpose of respiration. The 

 gills of fishes, therefore, offer an eligible situation for their development, 

 as do the branchiae of other animals ; or they are sometimes found 

 attached in great numbers to the interior of the mouth in various fishes, 

 deriving from its vascular lining, or from the abundant secretions met 

 with in such a locality, a plentiful supply of food, while they are freely 

 exposed to the currents of water which the mode of respiration in the 

 fish brings in contact with them. 



(1082.) The least-elaborately organized of these animals exhibit ex- 

 ceedingly grotesque and 



singular shapes, resembling Fig. 218. 



imperfect embryos rather 

 than mature beings, the 

 first buddings of external 

 limbs, in the earlier period 

 of foetal development, imi- 

 tating not very remotely 

 the appearance of the ru- 

 dimentary appendages re- 

 presented in the annexed 

 figure* (fig. 218). 



(1083.) A great number 

 of species of these para- 

 sites, generally described 

 under the name of Ler- 

 neans, have been observed 

 by authors, and it would 

 seem, moreover, that each 

 is peculiar to a particular Lerneans. 



kind of fish. The variety 



exhibited in their outward forms is, of course, exceedingly great ; but 

 the examples depicted in the figure, namely the Lerncea gobina, found 

 in the branchiae of Coitus Gobio, and Lerncea radiata, which infests the 

 mouth of Coryphwna rupestris, will make the reader sufficiently ac- 

 quainted with their general appearance and external structure. In the 

 former parasite, of which a posterior and an anterior view are given 

 in fig. 218 (a, b), the appendages seen upon the head and sides of the 

 body answer the purpose of hooks or grappling organs, whereby the 

 creature retains its position ; and so firm is its hold upon the delicate 

 covering of the gills, that, even after the death of the fish, it is not easily 

 detached. In the second example (c, cZ), besides the rudimentary limbs, 

 the lower surface of the head and ventral aspect of the body (d) are 

 covered with sharp spines, calculated to increase very materially the 

 * Miiller (O. F.), Zoologia Danica, 1788. 



