60 NEW SPECIES OF CALIGUS. 



thicker, towards the propulsion feet. A fin somewhat similar but 

 much smaller is seen at the anterior extremity of the carapace, 

 between the two lunules. 



The upper side of the cephalothorax appears to be composed 

 of nine plates of shell ; at least there are depressions which would 

 seem to indicate that the shell is separated into that number 

 of parts. 



At first it was concluded that this was a species oi Lepeoptheirus ; 

 but from the presence of the two lunules, or sucking-discs, which 

 I believe only the Caligus has, it must belong to the latter species. 



The fish upon which these Caligi were discovered did not 

 appear to be in the slightest degree discomposed by their pre- 

 sence ; neither did they seem to inflict any injury upon their host, 

 or even to attach themselves permanently to any one special spot 

 or portion of his body ; but just to move about with greater or 

 less briskness as humour or accident dictated. 



What purpose in the economy of Nature such creatures can 

 serve is very mysterious. For these, the Caligi and Lepioptheiri 

 especially, are not found on unhealthy fish, but are rather proofs 

 of good condition and vigour. The indications of disease are 

 shewn by quite a different class of Hving things — by other species 

 of parasites quite unlike these, and by various kinds of fungoid 

 growth ; — but the fact that a condition of health, sound constitu- 

 tion, and perfect vigour should be indicated by the necessary 

 presence of any sort of parasitical animals, is a mystery in nature 

 which remains yet unsolved. 



EXPLANATION OF PLATE G. 



Fig. 1. — Female Caligus, undescribed species. 



Fig. 2.— Male ditto ditto. 



Fig. 3. — Mouth-organs of Lepeoptheirus Stromii ; general 



view, X 200. 

 Fig. 4. — Recurved teeth in mouth, more highly magnified. 

 Fig. 5. — Eye of Caligus, with double lens. 



