﻿MONOTREMES. 229 



modification in the usually accepted classification is advis- 

 able, there would seem to be considerable justification for the 

 removal of the Monotremes from among the Mammals to form 

 a separate class by themselves ; althougli such a radical change 

 should only be made after much deliberation and careful weigh- 

 ing of evidence. 



As characters which may be regarded as distinctive of the 

 Monotremes as an Order, in contradistinction to a Sub-Class, 

 the following may be noted : — 



In both the two existing families the males are provided with 

 a perforated spur on the inner side of the heel, connected with a 

 gland behind the thigh, the function of which is not yet 

 clearly understood. Although the ass imption that this gland 

 is poison-secreting has not been proved to be true, it has been 

 suggested that during the breeding season if such a function 

 were developed it might be advantageous to the males in their 

 conflicts for the possession of the females. 



Like the Marsupials, the Monotremes possess the so-called 

 marsupial, or epipubic bones attached to the anterior rim of 

 the pelvis. In all the muzzle is produced into a beak, which 

 may be either flattened or cylindrical ; and true functional teeth 

 are absent at least in the adult. The external aperture of the 

 ear opens on the surface of the head without any trace of a pro- 

 jecting conch ; the short and powerful limbs are of subequal 

 length, and adapted for digging ; and the tail is either short 

 and broad, or rudimental. 



That the existing Monotremes are specialised survivors of an 

 extremely ancient stock, is rendered evident on the one hand 

 by their peculiar beaks and the absence of teeth in the adult 

 or throughout life, and on the other by their low general or- 

 ganisation and their marked indications of affinity with the 

 lower Vertebrates. On the whole, their nearest allies among 

 the latter seem to be a group of Reptiles whose remains are 



