HIGH SCHOOL ZOOLOGY. 267 



graph ; competition foi' food on the part of animals having led 

 to the necessity for the complex mechanisms of the muscular 

 and nervous systems. 



The functions of the nervous system include all those pro- 

 cesses, which, in their elementary forms, appear as the simplest 

 kinds of " reflex action," such as, for example, the contraction 

 of the Amceba on irritation, but pass by easy transitions 

 through higher forms, till those extremely complicated inherited 

 reflexes, which we call "instincts," are reached, and even those 

 higher processes, which we ascribe to the " intelligence" of 

 animals. Such psychical processes, from the simplest to the 

 most complex, form the subject-matter of Animal Psychology 

 and Sociology. 



(c) The third group of functions is formed by those which 

 refer to the producti n of new individuals. Very close paral. 

 lels are offered by the vegetable and animal kingdoms in re 

 spect to these, and multiplication by division (sepai'ation of the 

 body into equal parts), the formation of buds (detachment of 

 smaller portions), or, finally, the detachment of i-epi'oductive 

 cells, and the formation of new individuals from eggs are to be 

 observed in both. Similar phenomena iif connection with this 

 group of functions are also to be studied in both ; such as (1) 

 the limited span of life of the individual ; (2) the tendency for 

 succeeding generations to increase in number ; (3) the ten- 

 dency of the offspring to inherit the form of the parent, and 

 yet (4) to vaiy considerably from that form. These phenomena 

 lead us to the discussion of various other aspects of Biology, in 

 the first place, of those which exhibit the relations of present to 

 preceding generations, viz.: Developmental, Palseontological and 

 Taxonomic aspects. 



(3) Developmental and Pal.eontological. 

 8. We know that the plants and animals living on the earth at 

 present are the descendants of the immediately preceding gene- 



