NASCENT ORGANS. 8$ 



make use of them, would still retain this organ as a 

 hydrostatic apparatus. And thus we find the air- 

 bladder to-day the homologue of the lung, but not 

 a remnant of a formerly functional lung, nor a 

 prophecy of a future lung, but a rudimentary be- 

 ginning, which is or has been capable of further 

 development. It is not, of course, claimed that such 

 has been the exact history of the development of 

 the lung, for of exact history we are profoundly 

 ignorant. The example has been taken as an illus- 

 tration of the sort of explanation which the evolu- 

 tion theory has to offer for nascent rudimentary 

 organs. It was the presence of this highly variable 

 air-bladder which enabled the early land animal to 

 leave the water, for a short time at first, but after- 

 wards for longer periods. The rudimentary lung, 

 or vascular air-bladder, did not appear in order that 

 animals might become air-breathers, but animals 

 became air-breathers to escape their enemies, as 

 soon as their air-bladders, varying by chance or 

 otherwise, enabled them to do so. This air-bladder 

 was the cause of air-breathing, but not, according to 

 the descent theory, created for this distinct purpose. 

 They were the predecessors, but not the prophecies, 

 of lungs. 



It is by no means always possible to determine of 

 a given structure whether it be an atrophied rem- 

 nant or a nascent organ ; and indeed sometimes it 

 may partake partially of both characters. It would 

 be expected that an atrophied organ would be very 

 similar in form to its developed homologue, but 

 much smaller, and with various parts lost or fused 



