24 STUDIES IN ANIMAL LIFE. 



assimilating surface to a complex apparatus serving 

 the functions of vegetative life. 



Now glance at the outer wall : from it also vari- 

 ous organs have gradually been wrought ; it has de- 

 veloped into muscles, nerves, bones, organs of sense, 

 and brain — all these from a simple homogeneous 

 membrane! , ■ 



With this bird's-eye view of the course of devel- 

 opment you will be able to appreciate the grand 

 law first clearly enunciated by Groethe and Von 

 Baer as the law of animal life, namely, that devel- 

 opment is always from the general to the special, 

 from the simple to the complex, from the homoge- 

 neous to the heterogenedus, and this by a gradual 

 series of differentiations* Or, to put it into the 

 music of our deeply meditative Tennyson, 



"All nature widens upward. Evermore 

 The simpler essence lower lies : 

 More complex is more perfect — owning more 

 Discourse, more widely wise." 



You are now familiarized with the words "differ- 

 entiation" and "development," so often met with 

 in modern writers, and have gained a distinct idea 

 of what an " organ" is, so that, on hearing of an 

 animal without organs, you will at once conclude 

 that in such an animal there has been no setting 

 apart of any portion of the body for special pur- 

 poses, but that all parts serve all purposes iiylis- 



* Goethe: Zur Morphologic, ISO! . VonBaee: ZurEntuddc- 

 elungsgescMchte, 1828. Part I., p. 158. 



