264 



CLASS AMPHIBIA. 



Fig. 142. — Skeleton ' o£ Menopoma 

 alleghaniensis (from Claus). Et orb- 

 itosphenoid ; F frontal ; Jl pelvic 

 girdle ; Jmx premaxilla ; J/.f maxilla ; 

 N nasal ; Ocl exoccipital ; P parietal ; 

 Pe prootic ; Pt pterygoid ; R ribs ; 

 S sacral vertebra ; Se scapula ; Ty 

 squamosal ; Vo vomer. 6 Hyoid appa- 

 ratus; Zb hyoid ; Kb branchial arches. 



gill-slits and gills, (2) a single 

 artery — the ventral aorta — alone 

 leaves the heart, (3) there are 

 only ten pairs of cranial nerves, 

 (4) the presence of a functional 

 pronephros in the larva, (5) the 

 sexual part of the kidney is 

 distinct from the testis and not 

 incorporated into it as an epidi- 

 dymis, (6) the character of the 

 ovum and the early develop- 

 ment, (7) the absence of an 

 amnion and allantois, (8) the 

 presence of functional lateral 

 line sense-organs. 



On tlie whole it will be gene- 

 rally admitted that they stand 

 nearer to fishes than they do 

 to the higher forms, and that 

 Huxley's inclusion of them with 

 Pisces in a group which he 

 called Ichthyopsida has a solid 

 basis of fact. Nevertheless it 

 must not be forgotten that the 

 higher Amphibia present certain 

 subtle features of approach to 

 the Reptiles which are not shared 

 by the lower members of the 

 group. We refer especially to the 

 asymmetry of the systemic aortic 

 arches in the Anura (j). 284), 

 and to the apparent abortion of 

 the sexual part of the kichiey in 

 the male Alytes (p. 293). 



In the main the Amphibia are 

 aquatic in their habits : the 

 majority live in or near Abater, 

 and in almost all the congress of 

 the sexee takes place and the 

 eggs are laid in water. But 



