34 ORGANIC EVOLUTION 



one another \ve have lately been able to appreciate more 

 than ever before. There seems to be some reason to believe, 

 though it is not yet proven, that every organ and cell in the 

 body so acts upon every other as to affect its behavior. 



This is well illustrated by the effects of extirpation of 

 organs. We do not know what effect the thyroid glands 

 have on the other organs of the human body, but if they be 

 removed or become badly diseased, we find there results a 

 profound disturbance of the functions of other parts of the 

 body, showing that the thyroid glands when present and nor- 

 mal probably exert some influence the absence of which from 

 the body is disastrous. There are many other organs whose 

 functions we do not understand, whose extirpation is seriously 

 injurious. Their influence upon other organs of the body 

 must be very important. The changes which follow the 

 destruction of the organs of reproduction are of especial 

 interest in this connection. In the common domestic 

 chickens the destruction of the testes in a young male pre- 

 vents the comb and wattles and spurs reaching their normal 

 size, the habit of crowing is given up, the characteristic 

 combative disposition of the male is lost. Likewise the 

 destruction of the ovaries in a young hen makes the comb 

 and wattles enlarge, the habit of crowing may be acquired, 

 and the disposition becomes more pugnacious. Here we 

 have a clear indication that the presence or absence of the 

 reproductive organs influences organs which seemed to 

 casual observation to be unrelated to them, namely the brain 

 (change of disposition), the comb and wattles upon the head, 

 and the spurs on the feet. Probably many other organs of 

 the body are equally influenced in ways not so readily ob- 

 served. 



