CHAPTER I. PROTOZOA 



SECTION A. THE PROTEOMYXA l 



IN the study of the Protozoa a number of forms are found 

 which are difficult to place in any of the larger orders or families. 

 The difficulty arises in many cases from what is called their 

 simplicity of structure, and partly from our ignorance of their entire 

 life-history. The more we learn of the structure of the Protozoa, 

 the more hazardous does it become to apply the expression " simple " 

 to any living organism, but what is really meant by the term 

 " simple " as applied to these organisms is that they exhibit no 

 definite structure or structures such as skeleton, flagella, or nuclei 

 that are so constant in their form and character that they can be 

 seized upon by the systematist and used for purposes of classifica- 

 tion. When characters of this description appear during one phase 

 only of the life-history of an organism they may indicate its 

 affinities if not its true systematic position, but when the life-history 

 is not completely known there may be no characters which can 

 possibly serve for placing the organism with others in any 

 system of classification. In the early history of Protozoology there 

 was a time when it was considered that some of the very small 

 and obscure organisms consisted of a cytode of protoplasm in 

 which there was no structure corresponding with the nucleus of the 

 higher organisms and cells. Such organisms were placed in a class 

 Monera by Haeckel in 1868. Subsequent researches proved that 

 in many of these organisms one or many minute structures occur 

 which give the same reactions as the chromatin of the nucleus, 

 and the conclusion was, in some cases too hastily, drawn that all 

 of them would in time be shown to be nucleated. Modern 

 researches on the nuclear structures of Protozoa have thrown 

 much light on this vexed question. They have shown that the 

 nucleus may discharge into the cytoplasm, or give rise by total 

 fragmentation to, a number of minute granules of chromatin the 

 chromidia and that these granules do not degenerate, but retaining 

 their vitality may again aggregate together in the formation of new 

 nuclei. There may thus occur in the life-history of the higher 

 Protozoa a stage which is strictly speaking non-nucleate (akaryote). 



1 By Prof. S. J. Hickson, F.R.S. 



1 i 



