FLIMMER-LA11V.E. 6 1 



having reached maturity the society dissolves. Each sepa- 

 rate cell still lives a while independently, grows, and changes 

 into a crawling Amceba. This afterwards assumes a globu- 

 lar form, and encases itself by exuding a structureless 

 integument. The cell now has just the appearance of a 

 common animal egg. After it has remained for a time in 

 this quiescent state, the cell breaks up, by means of con- 

 tinued division, first into 2, then into 4, 8, 16, 32 cells. 

 These again arrange themselves so as to form a globular 

 vesicle, put forth cilia, and bursting the encasing integu- 

 ment, swim about in the same Magosphcera-form from 

 which we started. This accomplishes the entire life-history 

 of this remarkable Primitive Animal. 141 



If we compare these permanent blastula-forms with the 

 freely swimming Flimmer-larvre or planula-condition, of 

 similar structure, of many other lower animals, we may 

 Avith certainty infer therefrom the former existence of a 

 primaeval and long-extinct parent-form, the structure of 

 which was essentially like that of the planula or blastula. 

 We will call this the Planaea, or Blastrea. The whole body, 

 in its fully developed condition, consisted of a simple hollow 

 globe, filled with fluid or structureless jelly, the wall of 

 which formed a single stratum of homogeneous cells, 

 covered with cilia. Many different kinds and species of 

 Plansea-like Primitive Animals must certainly have existed 

 and formed a distinct class of Protozoa, which we may call 

 Flimmer-swimmers (Planceada). A remarkable proof of the 

 natural philosophical genius with which Karl Ernst Baer 

 penetrated into the deepest secrets of the history of animal 

 evolution, is that, as early as the year 1828 (ten years before 

 the cell-theory was established), he guessed the significance 



