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 Goethe 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 heterogeneous, 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 indis- 



* GOETHE: Zur Morphologie, 1807. VON BAER: Zur Entwick- 

 elungsgeschichte, 1828. Parti., p. 158. 



