Miscellaneous. 



441 



developed at all, — they may be consequences of a law of development, 

 and not active organs, or parts in the organism in which they are found. 

 Thus in the present state of physiology, it would be rash to draw the 

 conclusion that the traces of the canals to which we referred as now 

 existing in marsupials, are certainly but the remains of what were fully 

 developed in their primeval types. We incline to the idea, and suggest 

 it to the consideration of those more conversant with such subjects; 

 but at the same time allow, that it is not a necessary consequence of 

 their existence, although it may be a probable one. So far, however, is 

 certain, that it forms a kind of connecting link between the respiratory 

 systems of marsupials and reptiles. But, in considering a matter such 

 as this, we must not confine our views to the respiratory system alone, 

 but must take into consideration the whole organization of the animal, 

 and the peculiar connection of its various systems, with their modes of 

 reaction. Viewing it in this light we find the animals in question 

 occupying only a low position in the scale of creation ; it is, therefore, 

 highly probable that they could live in an atmosphere considerably 

 worse than they now enjoy. Here, again, I must apologise for want of 

 a few experiments which would have at once decided the question ; but 

 the short time which has elapsed since I was requested to prepare this 

 lecture for you, has prevented me from procuring an opossum to treat 

 to such an atmosphere. Any of you who may have such an animal 

 may easily satisfy yourselves by a few experiments. 



But whilst wandering through these ancient lands, how comes it that 

 we have not met any of the winged tribes ? Forests are there to form a 

 habitation — insects abound to afford them food; the genial climate 

 or the smiling face of nature invites them to sing its praises. But in 

 vain we penetrate the deep recesses of those ancient forests to discover 

 traces of the feathered songsters of former days. We search the shores 

 and the rivers to find aquatic birds feasting on the fishes which so 

 abound, but we are scared away by the saurians which line their banks. 

 We enter the forests, and meet nought but the monstrous pterodacty- 

 lus sailing along on its filmy wings. If birds existed, where are their 

 remains ? Though rare, still we find them scattered throughout the 

 tertiary and modern lacustrine deposits. Why is there not a single 

 evidence of their existence in all the secondary strata? Simply because 

 (if our view of the state of the atmosphere be correct) they could not 

 have existed. Birds require a very large supply of oxygen for the 

 support of their vital functions, and are peculiarly susceptible to the 

 effects of an excess of carbonic acid. Neither of these conditions being 

 yet favourable, nature was not fitted to receive them. 



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