Evolution of Animals 493 



sweat and mucous glands along either ventro-lateral side may 

 have deepened, enlarged, and changed more and more the 

 secretion from a mucous to a lacteal condition. It may even 

 be that the large " Kornchendrusen " of Engelmann which occur 

 along the center and sides of higher urodeles, which contain a 

 milky-like secretion, and which in living forms seem to be a 

 poisonous excretory and defensive substance, may have had its 

 secretion primitively different or gradually changed, so as to 

 utihze it for nourishment of the young. Such structures, alike 

 morphologically and physiologically, furnish a basis and starting 

 point amongst urodeles for mammary glands, such as we have 

 no trace or suggestion of amongst reptiles. 



In spite therefore of many apparent points of morphological 

 contact between reptiles and mammals, we would strongly 

 second Huxley's position, that it is amongst the urodele Ba- 

 trachia that we have to look for progenitors of the primitive 

 mammals. The latter we will now study somewhat in detail. 



As Cope, Osborn, and others have emphasized, the primitive 

 marsupials were on the whole generalized types, from which 

 higher and specializing groups have evidently started. In 

 addition to features already observed while comparing the 

 above groups, and which eminently favor the view that the 

 marsupials are the starting point for at least most of the mam- 

 mals, the following comparative details deserve special at- 

 tention : 



When the still immature embryos are transferred to the 

 maternal teats they develop a sucking mouth that at once 

 reminds one of the like organ in many larval stages of batrach- 

 ians, of the larval mouth pads of Amhlystoma, the oral attach- 

 ing cirri in Triton, Spelerpes, and other genera, the suctorial 

 disk of cyclostomes, and the labial expanse of many nemerteans. 



As regards the mamniie, the following seems a likely view 

 as to their number and distri])ution. If in ancient viviparous 

 types, that conformed somewhat to Salaviandra vwcnlob-a, 

 several eggs matured in the uterus up to a certain stage, and 

 were then set free to be retained along the curled-together 

 abdomen of the mother, the sucking action of these might 



