EPIZOA. 



129 



perfect embryos than mature beings ; the first buddings of external 

 limbs in the earlier period of foetal developement imitating not 

 very remotely the appearance of Fig. 52. 



the rudimentary appendages re- 

 presented in the annexed figure* 

 (Jig. 52). But this resem- 

 blance is not confined merely to 

 a fancied similarity in outward 

 form ; it exists in the physio- 

 logical relation that there is 

 between the embryo and the 

 Epizoon, and seems dependent 

 upon that great principle which 

 inseparably connects the perfec- 

 tion of an animal with the cha- 

 racter of its nervous system : 

 the nerves of the Epizoa are 

 simple filaments, the ganglia 

 being indistinct or scarcely de- 

 veloped ; and the imperfection 

 of the limbs is a necessary consequence. In the same manner, in 

 the earliest stages of foetal growth, when we know that the nerves are 

 as yet but mere threads, it is interesting to observe the resemblance, 

 even in outward appearance, between the embryo in this transitory 

 stage of its growth, and the permanent condition of the Epizoa 

 which we are considering. 



(1 69.) A great number of species of these parasites, generally de- 

 scribed under the name of Lerneans, have been observed by authors, 

 and it would seem indeed that each is peculiar to a particular kind of 

 fish. The varieties observable in their outward form are, of course, 

 exceedingly great; but the examples depicted in the figure, namely, 

 the Lerneea gobina, found in the branchiae of Coitus Gobio and 

 Lernaa radiata, which infests the mouth of Coryphcena rupestris, 

 will make the reader sufficiently acquainted with their general ap- 

 pearance and external structure. In the former parasite, of which an 

 anterior and posterior view are given in the engraving (a, b), the 

 appendages seen upon the head and sides of the body answer the 

 purpose of hooks or grappling organs, whereby the creature re- 

 tains 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 



* Miiller (Othone Frederico) Zoologia Danica, 1788. 



