38 COBBOLD, OX GYRODACTYLVS ELEGANS. 



"II. The clasping apparatus at tLe posterior end of tlie 

 hodx, must^ in an animal so soft and constantly exposed to 

 the passage of regular currents, be comparatively strongly 

 developed, and accommodated to the peculiar dwelling places ; 

 and probably the latter supply a reason why there should be 

 so great a variety in the mechanism of the hooks belonging 

 to the disc. 



" III. This hooked apparatus affords a very yaluable means 

 of diagnosis for the determination of the species with mathe- 

 matical precision. This may be accomplished by observing 

 whether there are two or four large hooks ; whether there be 

 one or two connecting portions, and by noticing their several 

 forms and relation to one another ; whether there are hook- 

 lets present or not, remarking in the first instance their 

 position, form and distribution, and so forth. 



" IV. The integument is sometimes wrinkled transversely, 

 at other times appearing to be smooth. 



" V. The muscular apparatus is sometimes very strongly 

 developed. In the majority of instances special muscles are 

 inserted into the handles of the hooks, and they are also very 

 frequently directed into the transverse muscles of the skin. 

 A retractor palparmn medhis, and protrusor penis, are found 

 in Gyrodadylus crassiusculus. 



"VI. The four so-called eye spots are observed on the 

 dorsal surface, at the fore part of all Gyrodactyli (with the 

 exception of G. elegaas) . As already taught by Siebold they 

 answer the purpose of light-refracting organs. The palpi 

 appear to be retractile touch-organs (seen to contain mus- 

 cular bundles in G. crassmscidus) , and extend more or less 

 prominently forward. 



" VII. The observations in regard to the alimentary canal 

 are at present incomplete, for only in the case of Gyrodactylus 

 cochlea was a single gullet demonstrable ; this was furnished 

 Avith epithelium, being tinged either yellow or brownish- 

 yellow ; it passed from before backwards, and was probably 

 provided with an anus, whilst, in all other instances, its 

 passage could not be traced. The reason of this arises from 

 the transparency of the intestinal contents, and from the 

 internal blending of the wall of the canals with the parenchy- 

 matous substance. The other organs likewise hinder our 

 observation. 



"VII. In three species of Gyrodactylus (G. cochlea, G. 

 crassh'.scidus, and G. tenuis) the generative organs are thus 

 disposed : — The ^-itelline organ is characterised by its botry- 

 oidal structure, and its round secretion-cells, which contain 

 granular matter ; these are so completely surrounded by an 



