Organisms Consisl'inrj of One Cell *27T 



interest, since the doctrine of evolution became establislied 

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

 organs which a])pear in the course of the individual di\(l()|)- 

 ment. Johnson gave special attention to two such organs 

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

 former is a canal in the endoplasm, just beneatli tlie aboral 

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

 the newly produced posterior zooid, its complete atrophy 

 occurring soon after fission. Johnson j)i'()ved it to originate 

 in connection with the contractile vesicle. 



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

 band 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 develo])ment 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 ''Emhrijolog?/' and ''Ontogeny'' Inevitahli) Used 

 hy Imrestigators of Protozoan lieproduction 



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 Protozoa speak of the ontogeny and embryogeiiy of 

 the creatures despite efforts like those quoted above to re- 

 strict the term to the metazoa. Looking at these illustra- 

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



