248 



THE FORMS OF CELLS 



[CH. 



Precisely the same series of unduloid forms may be traced in 

 even greater variety among various other families or genera of the 



Fig. 76. Various species of Salpingoeca. 



ft 



Fig. 77. Various species of Tintinnus, Dinobryon and Codonella. (After 

 Saville Kent and others.) 



Infusoria. Sometimes, as in Vorticella itself, the unduloid is seen 

 merely in the contour of the soft semifluid body of the living 

 animal. At other times, as in Salpingoeca, Tin- 

 tinnus, and many other genera, we have a distinct 

 membranous cup, separate from the animal, but 

 originally secreted by, and moulded upon, its 

 semifluid living surface. Here we have an excellent 

 illustration of the contrast between the different 

 ways in which such a structure may be regarded 

 and interpreted. The teleological explanation is 

 that it is developed for the sake of protection, as a 

 domicile and shelter for the little organism within. 

 The mechanical explanation of the physicist (seeking 

 only after the "efficient," and not the "final" cause), is that it is 



Fig. 78. 

 Vaginicola. 



