SYNOPSIS 391 



VIII. UNICELLULAR AND DIPLOBLASTIC ANIMALS. 



PAGE 



a. In plants there is a clear transition from unicellular forms to 



solid aggregates, but in animals the connection of the 

 gastrula with unicellular forms is uncertain 260 



b. Two hypotheses of the origin of the gastrula : (i) from a 



colony of unicellular zooids ; (2) from a solitary multi- 

 nucleate but unicellular form . 265 



C. Other matters of general importance, such as the composition 

 and properties of protoplasm, cellulose, chlorophyll, starch, &c. : 

 metabolism : holozoic, holophytic, and saprophytic nutrition : intra- and 

 extra-cellular digestion : amoeboid, ciliary, and muscular movements : 

 the elementary physiology of muscle and nerve : parasitism and sym- 

 biosis : asexual and sexual generation : and the elements of embryology 

 are discussed under the various types and will be most conveniently 

 referred to by consulting the Index. 



