414 Causes and Course of Organic Evolution 



most of the higher groups sprang. The tendency of some of 

 these to form not merely fine ciha of compHcated relation to 

 the cell and its nucleus, but also strong tactile bristles disposed 

 at definite points, deserves emphasis. The next step therefore 

 in tlie main line of ascent is to ascertain how and by what 

 stages the ciliate infusorian organism became multicellular, 

 and what are now the simplest representatives of that multi- 

 cellular state. 



But for the entire group of the Spongida we evidently must 

 look not to the Infusoria ciliata, rather to the flagellate infus- 

 orians or Mastigophora. And in such semicolonial, semimulti- 

 cellular genera as Proterospongia and Phalansterium we have 

 examples of what may have been during the mid- or late 

 archsean epoch abundant evolving types. The unicellular 

 embryo of these, early segmenting and attaching itself, started 

 a zoological cul de sac that has persisted to this day. 



As regards the main line of evolutionary progress through 

 ciliate infusorians, the first morphological advance we believe 

 is in the enlargement of each cell organism or bio-cognitic 

 mass, and the formation of several nuclei that become bio- 

 cognitic centers in it. 



Next in the intimate relation of each organism to its envir- 

 onment tliis is beautifully assured, first by the usually ex- 

 tremely flexible and adaptable body mass; second, by the 

 ciliary investment; third, by the frequent presence of special 

 centralized cirrhi near or round the mouth or head end, along 

 the body, or posteriorly; and, fourth, by the formation in some 

 genera like Trachelius, Ileonema, and Dileptus of a preoral 

 process of a tactile i)roenvironal nature. 



Again the great majority of the Infusoria are markedly 

 bipolar and have a definitely restricted sucking mouth, an 

 endoplasmic biotic mass for digestive and general vegetative 

 activities, and occasionally even a restricted anal region. 



The abundance and uniform character of the cilia over the 

 cells of the embryo or even the adult animal, in many divisions 

 of invertebrata, and their retention over soft protected sur- 

 faces of the vertebrata would lead us to suppose that possibly 



