440 



Miscellaneous. 



come in collision with the plans of the intelligent Creator to remove 

 from the atmosphere by means of organic life the excess of car- 

 bonic acid. 



From these facts we see that reptiles could have had no difficulty 

 in living in an atmosphere containing less oxygen than at present; 

 but we find that in the oolitic period, a particular kind of quadruped 

 existed. This seems to have been a marsupial animal allied to the 

 didelphys. It was evidently an insectivorous animal, from the con- 

 formation of its jaw bones found in the Stonesfields oolitic beds, 

 where the elytra of land beetles are found accompanying them. Now 

 can we find nothing in the respiratory system of the marsupials 

 which would lead us to believe that they might have been in an 

 atmosphere such as we have supposed to exist? The marsupials of 

 course breathe, like other mammals, like man himself, by the lungs 

 alone; and if any peculiarity of the respiratory system existed in 

 the primeval didelphys, we could scarcely expect to find anything 

 but mere traces of it in its modern congeners, changed as they must 

 have been to suit the varied conditions of the atmosphere ; but let 

 us try to discover whether such traces may not have been pre- 

 served. 



Now in saurians, chelonians, and fishes, two canals are observed 

 to issue one on each side of the anus into the peritoneum, that is to the 

 external surfaces of the viscera. Their use seems to be to carry on 

 a partial aquatic respiration, or, in other words, to supply aerated 

 water to the blood circulating in particular vessels. It would also 

 appear that more highly oxygenated blood is required for those vessels 

 which supply the brain. This adjunctive respiratory system is supposed 

 to subserve this purpose. Its presence evidently indicates a want of 

 oxygenation of the blood. Now it is very remarkable that traces of 

 these canals exist in the marsupials. Mere traces, however, of any 

 structure, do not subserve functions : they may be considered in two 

 lights, either as remains of what have been, or as general indications of 

 some of the phases through which all the parts of organized bodies 

 pass during developement. Before drawing conclusions regarding the 

 full development of these traces in former types, we must also remem- 

 ber, that no class, order, family, or genus of animals or plants, ever did 

 or ever can pass, beyond the bounds of the type after which they 

 are formed. Again, traces do not necessarily indicate that a,full develop- 

 ment once existed in the family ; it only proves, that such a family was 

 or is made after the type of some division or other of the animal or 

 vegetable kingdom ; hence the traces may never have been fully 



