416 Causes and Course of Organic Evolution 



and then to the adult. But the Hnes of stereoenergesis in 

 the Rotifera remain fundamentally as in ciliate Infusoria. 

 Wliile such is true, however, the writer is deeply sensible that 

 no single organism now exists which would readily bridge over 

 the highest existing infusor with the simplest rotifer. But this 

 is not surprising when we bear in mind the wide and deep or- 

 ganic gaps which exist all along the biologic scale. 



' c.d.^ 



me. n. 

 mi.ri: 





%. 





ai.~- 



Fig. 14. — a, ciliate infusor; &, rotifer; c.d., ciliated disc; m, mouth; me.n., 

 meganuclei; mi.n., micronuclei; n., nuclei; ph., pharynx; d.a., digestive area; I., 

 liver; e.v., excretory vacuoles; ex., excretory canals; a, anus; l.m., longitu- 

 dinal muscles; b, brain; e, eyes. 



So, we would accept it as likely that continuous morphological 

 progress was made from higher ciliate infusorians to simple 

 rotifers. During the process, in addition to the establishment 

 of a soft and faintly differentiated system of ecto-, meso-, and 

 endodermal cell layers, as traced by Zelinka, there further origi- 

 nated that double swelling and ingrowth of ectodermal cells in 

 the head segment that formed the commencing nervous system. 



As regards its origin and value, though the following is only 

 in the nature of a vague surmise, it might be recalled that 



