ANIMAL DEVELOPMENT 



CHAPTER LIII 



ANIMAL DEVELOPMENT— GENERAL PRINCIPLES- 

 VEGETATIVE PROPAGATION 



The preceding sections of this worlv have been devoted to 

 Classification, and to those functions that maintain the Hfe of 

 the individual. We may now instructively consider the various 

 means by which the continuance of the species is provided for. 

 The Development of the individual, of course, includes a con- 

 sideration of all the stages through which it has to pass 

 before becoming adult, and might with propriety be considered 

 under the heading of Life- Histories. But there are reasons 



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which make it desirable to treat Development and Life- 

 Histories as distinct sections. Under Development will be con- 

 sidered certain general principles as well as facts that can only 

 be studied in the laboratory by means of the microscope, and 

 technical methods associated with its use. The succeeding sec- 

 tion on Life- Histories will broadly treat of facts which can be 

 to a large extent made out by field naturalists, though many 

 details can only be fully elucidated by work in the laboratory. 

 And in that section it will also be convenient to deal with such 

 topics as Protection of Eggs and Young, and Animal Dwellings, 

 for these, of course, have an important bearing upon life- 

 histories. 



GENERAL PRINCIPLES OF DEVELOPMENT 



All the different ways by means of which fresh individuals 

 come into existence can be regarded as varieties of what may 

 broadly be termed ovei'growth. Every animal in the course of 

 its existence builds up food into living body-substance, and this 

 in its turn manufactures those components of the body which are 



