410 



THE FORMS OF CELLS 



[CH. 



being also surfaces minimae areae, were available, the unduloid was 

 manifestly the one permitted, and ipso facto caused, by the dimen- 

 sions of the organism and other circumstances of the case. And 

 just as the thickness or thinness of the pellicle 

 was obviously a subordinate matter, a mere 

 matter of degree, so we see that the actual 

 outhne of this or that particular unduloid is 

 also a very subordinate matter, such as physico- 

 chemical variants of a minor order would suffice 

 to -bring about; for between the various undu- 

 loids which the various species of Vorticella 

 represent, there is no more real difference than 

 that difference of ratio or degree which exists 

 between two circles of different diameter, or 

 two hnes of unequal length. 



In many cases (of which' Fig. 129 is an 

 example) we have a more or less unduloid form 

 exhibited not by a surrounding pelHcle or shell, 

 but by the soft protoplasmic body of a ciliated 

 organism; in such cases the form is mobile, 

 and changes continually from one to another 

 unduloid contour according to the movements 

 of the animal.* We are deahng here with no 

 stable equihbrium, but possibly with a subtle 

 problem of ''stream-lines," as in the difficult 

 but beautiful problems suggested by the form 

 of a fish. But this whole class of cases, and 

 of problems, we merely take note of here; we shall speak of them 

 again, but their treatment is hard. 



In considering such series of forms as these various unduloids we 

 are brought sharply up (as in the case of our bacteria or micrococci) 

 against the biological concept of organic species. In the intense 

 classificatory activity of the last hundred years it has come about 

 that every form which is apparently characteristic, that is to Say 

 which is capable of being described or portrayed, and of being 



* Doflein lays stress, in like manner, on the fact that Spirochade, unlike 

 Spirillum, "ist nicht von einer starren Membran umhiillt," and that waves of 

 contraction may be seen passing down its body. 



Fig. 129. Trachelo- 

 phyllum. After 

 Wreszniowski. 



