Organisms Consisting of One Cell 271 



10, the body of whicli is sharply difFerentiated into the three 

 distinct parts called the deutomerite, protomerite and epi- 

 merite,^'^ (the latter being a fixation organ of greatly varied 

 form in different species, and often highly specialized), must 

 imply an ontogeny of no mean extent? Nor are we any 

 longer without knowledge, at least in outline, of the develop- 

 mental series in this part of the sporozoan cycle for several 

 other series. The investigations of Leger and Dubosq are 

 especially noteworthy in this connection. From their ac- 

 count of the development of Pyxinia mobuszi we learn that 

 in this species the full grown animal, the slender epimerite 

 not included, is five times the length of the sporozoite ; and 

 the epimerite attaining a length greater than that of the 

 rest of the animal, penetrates through the entire length of 

 the epithelial cell of the intestine of the host. The whole 

 of the adult animal except the epimerite projects free into 

 the intestinal cavity. 



Misuse of the Term "Ontogeny/'" 



I give only one other quotation showing the extent to 

 which this obscuration of the facts of protozoan develop- 

 ment has gone in the interests of cellular elementalism. This 

 quotation is specially telling because it is genuinely up to 

 date and displays the extremity of the tendency by not be- 

 ing restricted to the meaning of the term embryogeny, con- 

 cerning the scope of which there is good historical and bio- 

 logical ground for difference of opinion, but goes to the 

 term ontogeny, concerning which there is no such ground. 

 ^'Ontogeny includes, as the developmental history (Entzcick- 

 lungsgeschichte) of the separate individual, all those 

 changes of form which the individual undergoes from its 

 point of origin, the fertilized egg cell, to the state of sexual 

 maturity." ^^ 



The terms ontogeny and ontogenesis, introduced into bi- 



