98 THE DATA OF BIOLOaY. 



and types of organisms, there are hidden fundamental simi- 

 larities ; and that the courses of development in such groups 

 and classes and types, though in many respects divergent, 

 are in some essential respects, coincident. The wide truths 

 thus disclosed, come under the heads of General Morphology 

 and General Embryology. 



By contrasting the structures of organisms, there is also 

 achieved that grouping of the like and separation of the 

 unlike, called Classification. First by observation of ex- 

 ternal characters ; second by observation of internal charac- 

 ters ; and third by observation of the phases of development ; 

 it is ascertained what organisms are most similar in all 

 particulars ; what organisms are like each other in every 

 important attribute ; what organisms have common primor- 

 dial characters. Whence there finally results such an ar- 

 rangement of organisms, that if certain structural attributes 

 of any one be given, its other structural attributes may be 

 empirically predicted ; and which prepares the way for that 

 interpretation of their relations and genesis, which forms an 

 important part of rational Biology. 



§ 39. The second main division of Biology, above de- 

 scribed as embracing the functional phenomena of organ- 

 isms, is that which is in part signified by Physiology : the re- 

 mainder being what we distinguish as Psychology. Both of 

 these fall into subdivisions that may best be treated sepa- 

 rately. That part of Physiology which is concerned 

 with the molecular changes going on in organisms, is known 

 as Organic Chemistry. An account of the modes in which the 

 force generated in organisms by chemical change, is trans- 

 formed into other forces, and made to work the various or- 

 gans that carry on the functions of Life, comes under the 

 head of Organic Physics. Psychology, which is 

 mainly concerned with the adjustment of vital actions to 

 actions in the environment (in contrast with Physiology, 

 which is mainly concerned with vital actions apart from 



