Organisms Consisting of One Cell 77 



interest, since the doctrine of evolution became established 

 in biology, is the fact of rudimentary, often transitory, 

 organs which appear in the course of the individual develop- 

 ment. Johnson gave- special attention to two such organs 

 in Stentor, the ring-canal and the peristomal-band. The 

 former is a canal in the endoplasm, just beneath the aboral 

 zone and running parallel with it. It is present only in 

 the newly produced posterior zooid, its complete atrophy 

 occurring soon after fission. Johnson proved it to originate 

 in connection with the contractile vesicle. 



The peristomal band (figure 12 p. p.) is a narrow, clear 

 hand inside of and running parallel with the aboral zone. 

 It also entirely disappears some time after fission. It is 

 believed to represent the peristome of the lower Heterotricha ; 

 that is, like so many rudimentary organs of the metazoa, 

 it is supposed to be an ancestral structure; to have, in other 

 words, a racial significance. It will be noticed even from 

 this imperfect description of division and development that 

 one of the two new animals, the posterior, resulting from 

 division, undergoes most of the development. It alone, or 

 very nearly alone, takes on new organs. It may therefore 

 very well be called the offspring, the anterior animal being 

 distinguishable as the parent. 



The Terms "Embryology" and "Ontogeny" Inevitably Used 

 bij Investigator* of Protozoan Reproduction 



The futility of supposing practical science will conform 

 to a definition drawn up in the interest of a grand theory 

 but in defiance of a great body of facts, could hardly find 

 better illustration than in the persistence with which students 

 of the Proto/oa speak of the ontogeny and embryogeny of 

 the creatures despite efforts like those quoted above to re- 

 strict the term to the meta/oa. Looking at these illustra- 

 tions a little further, let us take Valentin Hacker's work on 



