22 STUDIES IN ANIMAL LIFE. 



extremely simple. No one now believes the clear 

 spaces visible in their substance to be stomachs, as 

 Ehrenberg believed ; and the idea of the Polygas- 

 trica, or many-stomached Infusoria, is abandoned. 

 No one now believes the colored specs to be eyes, 

 because, not to mention the difficulty of conceiving 

 eyes where there is no nervous system, it has been 

 found that even the spores of some plants have 

 these colored specs, and they are assuredly not eyes. 

 If, then, we exclude the highly-organized Ratifera, 

 or "Wheel Animalcules," which are genuine Crus- 

 tacea, we may say that all Infusoria, whether they 

 be the young of worms or not, are of very simple 

 organization. 



And this leads us to consider what biologists 

 mean by an organ : it is a particular portion of the 

 body set apart for the performance of some particu- 

 lar function. The whole process of development is 

 this setting apart for special purposes. The start- 

 ing-point of Life is a single cell that is to say, a 

 microscopic sac, filled with liquid and granules, and 

 having within it a. nucleus, or smaller sac. Paley 

 has somewhere remarked that in the early stages 

 there is no difference discernible between a frog and 

 a philosopher. It is very true truer than he con- 

 ceived. In the earliest stage of all, both the Ba- 

 trachian and the Philosopher are nothing but single 

 cells, although the one cell will develop into an 

 Aristotle or a Newton, and the other will get no 

 higher than the cold, damp, croaking animal which 



