FISHES. 



81 



in the research garden attached to the Rouen ento- 

 mological laboratory the snails were entirely exter- 

 minated in 1891, as a result of introducing a hundred 

 toads and ninety frogs. 



Fig. 52. — Natterjack (Sw/o calamiia). 



CLASS V. : PISCES (FISHES). 



Cold-blooded Vertebrates (p. 19), which breathe 

 by gills during their whole life. The heart consists 

 only of a single ventricle and a single auricle (p. 18). 

 The head passes immediately into the body without 

 any intervening neck. Fishes move chiefly by means 

 of the tail, at the end of which there is a tail-fin. 

 This and the doi'sal and anal fins lie in the median 

 plane of the fish, while the pectoral fins, which are 

 attached to the skull in bony fishes, and also the 

 ventral fins, are paired structures more or less com- 

 parable to the fore and hind limbs of higher verte- 

 brates. The skeleton of most fishes (pike, perch, carp, 

 eel, plaice) is bony ; but in a few subdivisions of fishes 



G 



