274 ZOOLOGICAL PHILOSOPHY 



animals neither have nor can have nerves ; moreover, those in which 

 nerves are just arising, do not yet possess a nervous system that fulfils 

 the conditions for the production of feeling. It is probable indeed 

 that, in its origin or primitive imperfection, this system has no other 

 faculty than that of exciting muscular movement. The faculty of 

 feeling therefore cannot be common to all animals. 



If it is true that every faculty that is hmited to certain Uving 

 bodies is based upon a special organ, as is everywhere found to be 

 the case, it must also be true that the faculty of feeUng, which is 

 clearly hmited to certain animals, is exclusively the product of a 

 special organ or system of organs, whose activities produce it. 



According to this principle, the nervous system constitutes the special 

 organ of feeling when it is composed of a single centre of communica- 

 tion and of nerves terminating it. Now it seems probable that it is 

 only in the insects that the nervous system attains a development 

 sufficient for the production of feeling, although still of a vague kind. 

 The faculty recurs in all animals of later classes in a regular progress 

 towards perfection. 



But in animals less perfect than insects, such as worms and radiarians, 

 if we do find traces of nerves and separated ganglia, there are strong 

 reasons for the presumption that these organs are only adapted to the 

 excitation of muscular movement, the simplest faculty of the nervous 

 system. 



Finally, in animals still more imperfect, such as the majority of 

 polyps and all the infusorians, it is quite certain that they cannot 

 possess a nervous system capable of giving them the faculty of 

 feeling, nor even that of moving by muscles : for them, irritability 

 alone takes its place. 



Thus feehng is not a faculty common to all animals, as has been 

 generally held. 



Sexual Reproduction. This is a special faculty which is in animals 

 nearly as general as feeling ; it results from an organic function, not 

 essential to life, the purpose of which is to attain the fertilisation of 

 an embryo which then becomes fitted for the possession of Ufe, and 

 for constituting after development an individual like that or those 

 from which it sprang. 



This function is performed at particular periods, sometimes regular 

 and sometimes not, by the co-operation of two systems of organs 

 called sexual, one being the male organs and the other female. 



Sexual reproduction is observed in animals and plants, but it is 

 linaited to particular animals and plants and is not a faculty common 

 to all these hving bodies ; nature could not have made it so, as we 

 shall see. 



