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1881.] NATURAL SCIENCES OF PHILADELPHIA. 4tl 



development between the reptiles and birds on the one hand and 

 the placental mammalia on the other. As is well known, in the 

 structure of its skeleton and generative apparatus, the Ornitho- 

 rynchus resembles ver}' closel}^ the reptile and bird, while, as we 

 have just seen, the foetal membranes of the Kangaroo recall the 

 corresponding parts in the reptilian-bird type and foreshadow 

 those of the placental mammal. If the parts in question have 

 been truthfully described and correctly interpreted as partly 

 bridging over the gap between the non-placental and placental 

 vertebrates, the}' supply exactl}'^ what the theory of evolution 

 demands, and fui-nish, therefore, one more proof of the truth of 

 that doctrine. 



