194 Dynamic Theory. 



eny to his host. It is not less remarkable that the larva of a certain fly, 

 the "Cuterebra emasculator, in very numerous instances, destroj'S the 

 testes of various American species of squirrel without affecting the other 

 vital functions. " (Semper.) 



The cause of the degradation and loss of functions in parasites and 

 co-operatives is and can be due to nothing else than disuse. If one 

 organ can become reduced to a rudimentary state by disuse, so may an}' 

 other or even all providing some means survives for the performance of 

 their functions, or so much of the functions as are necessary to the 

 growth of the animal to maturity, and the formation of the eggs and 

 embryos for the next generation. It is related by Caleb Wright that in 

 India there have been many religious devotees who have rendered one 

 arm, and in some cases both arms, perfectly rigid and functionless by 

 holding them aloft in one position for a number of years. At first it is 

 necessary to lash the arms in the upright position, as it is not possible 

 to keep them so voluntarily, but in a short time the muscles and sinews 

 ^become rigid and beyond voluntary control. Of course, a person so 

 ; situated is unable to help himself to food or otherwise, and must be 

 served by others as gullible though less devoted than himself. If we 

 should imagine the process of self -disuse carried somewhat further, and 

 the subject, instead of taking his food in the usual way, to receive a 

 perpetual transfusion of blood from another person of sufficient health 

 and strength, then the digestive apparatus of the recipient might lie dor- 

 mant all his life, and his stomach, with its appendages, and the respira. 

 tory machinery, might become rudimentary. Extravagant as this seems 

 it is just what takes place in the case of the Rhizocephala and some 

 other crustacean parasites. However sweeping the degradation and 

 elimination or substitution of functions, the reproductive organs are al- 

 ways excepted. These obviously can never be superseded by proxy or 

 substitution, and never are or can be aborted without the extinction of 

 the race. All the activities of life refer to the preservation of this 

 thread of vitality from generation to generation. And the machinery 

 for the preservation of this thread is the only thing which is absolutely 

 essential in anatomical structure, and in cases of degradation, nature 

 will sometimes let everything go but that senses, brains, muscles, 

 stomach and intestines. An animal race in the condition of these para- 

 sites has returned to first principles. The long process or selection by 

 which with differentiation and heredity it acquired and maintained a 

 complicated anatomy and functions has all been undone, unraveled, as 

 it were. Every accessory and subordinate function has been lost ; only 

 the two great principles of animal existence, viz. , accretion and repro- 

 duction, remain in their simplest form the two principles which 

 include all the necessary functions of existence from which and within 



