Baer was concerned with the question of the relation of the 

 instinct for self-preservation to the sexual instinct, and 

 in connection with this he touched upon a question which 

 worried him, on the possibility of including the understanding 

 of purpose in a sphere of strict scientific investigation. 

 His considerations are discussed below. 27 



In the concluding chapter of his work Baer again noted 

 the importance of the discovery of paedogenesis for under- 

 standing the idea of parthenogenesis and the alternation of 

 generations. Understanding of these phenomena required 

 systematic examination of different forms of reproduction. 

 "I sought," Baer wrote, "to look through all that had been 

 written on this subject, as in a consultation with myself— a 

 consultation which may prompt more young investigators to 

 attempt to make similar comparisons that would also be useful 

 for them. During this, difficult tasks appear which we must 

 trace more closely" (p. 70) . To these tasks Baer related the 

 experimental investigations of the external conditions upon 

 which the parthenogenesis of Aphidae and the paedogenesis of 

 cecidia occurs. By means of these experiments, Baer supposed, 

 it could be elucidated why, in apparently related species of 

 medusa, one species immediately forms sexually mature medusa 

 from the swimming larvae and the other goes through the 

 sessile stage which is the budded strobila. 



To these facts and considerations Baer gave the following 

 resume: 



Organic bodies possess the ability to self-develop 

 by action intrinsic to them, as soon as they have 

 the possibility of receiving the necessary material. 

 In addition, they still have the ability to produce 

 new individuals. (p, 72) 



Self -development moves from absolutely simple forms 

 and elementary parts by gradual transformations . „ . . 

 The sequence of these changes is called in scientific 

 terms development, and in ordinary term life, growth; 



27. See Chapter 24 



478 



