DK. THEODOR NEUMANN. 213 



are no longer able to lead such a free life as the others 

 before mentioned, and they wonld surely perish if they 

 should become separated from their abode. 



We must not think, however, that these two classes 

 are really the only ones to be found, nor that they are 

 distinctly separate. There are many connecting links 

 between both; in other words, there is no sharp dividing 

 line between them, but many intermediate forms may be 

 reckoned with one class just as well as with the other. 

 Even more remarkable is the fact that a large part of 

 such parasites as seem most settled in their habits 

 change them during certain periods of their lives to 

 such an extent that they begin a free life again. For 

 some of them this change is really necessary, and occurs 

 regularly from generation to generation. We shall look 

 into these peculiarities more closely later on, after we 

 have answered one more question, namely, how was 

 parasitism developed from the ordinary forms of animal 

 life? Investigation reveals to us the fact that it is 

 really nothing specific, but only a certain modification 

 of general animal life, connecting with it in different 

 ways and at different points. Some animals are at first 

 living free, then as parasites, while others show us 

 through their relatives a more or less uninterrupted tran- 

 siiion to parasitic life; in short, we see that this is not a 

 life of a peculiar character, but only a special feature 

 which was gradually formed from free life by adaptation 

 to pieculiar conditions of existence. It is an axiom now- 

 a-days in the scientific world that parasitism, never 

 sharply distinguished from free life, can also never have 

 been a peculiar division of it, but must have developed 

 from it gradually. The way in which this transforma- 

 tion took place lies rather plainly before us. We may 

 assume the following: Some small animal of low or- 

 ganization feeds on other little animals which it catches, 

 overpowers and devours just as happens now-a-days. 



151 



