Organisms Consisting of One Cell 271 



10, the body of which is sharply differentiated into tlie three 

 distinct parts called the deutonwrite, protomerite and cpl- 

 merite,^'^ (tlie latter being a fixation or^^an 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 outhne, of the develoj)- 

 mental series in this part of the sporozoan cycle for several 

 other series. The investigations of Leger- and l)ubos(j are 

 especially noteworthy in this connection. From their ac- 

 count of the development of Pyxmia mbbuszi we learn that 

 in this species the full grown animal, the slender epimerite 

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

 the ejjimerite 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 tu 

 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 tht- 

 term ontogeny, concerning which there is nq such ground. 

 ''Ontogeny includes, as the developmental history {Kntzcich- 

 lungsgeschichte) of the separate individual, all those 

 changes of fonn 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- 



