CHAPTER XII 



REPRODUCTION AND SEX 



In the various animals which we have so far studied, we 

 have come across a number of examples of 

 Reproduction : reproduction, occurring in various ways and in 

 Asexual. different circumstances. It will be well at this 



stage to consider the process from a broad 

 point of view. We have seen (pp. 7-9) that the essence of 

 every act of reproduction is the origin, by fission from the 

 body of an animal, of a reproductive body, and the develop- 

 ment of the latter into the likeness of its parent, and that a 

 process of reproduction is said to be sexual or asexual 

 according as the reproductive body does or does not under- 

 go the process known as conjugation before it develops. 

 Reproductive bodies which differ thus in their behaviour 

 have, with few exceptions, a corresponding difference in 

 their constitution. This appears clearly on comparing 

 the two kinds of reproduction as they occur in Hydra. 

 Asexual reproduction is relatively a simple matter. It 

 consists in the formation of a reproductive body known 

 as a bud and its fission from the body and develop- 

 ment, although in Hydra the structural part of the 

 development is completed before fission takes place. 1 

 In the bud there are from the first both differentiated 

 energids — the ectoderm and endoderm cells derived from 

 the parent body — and energids which are undifferen- 

 tiated in the sense in which we have used this word in 

 considering the germs of the frog (p. 121), 2 for the bud 



1 Except in the case of longitudinal and transverse fission. 



2 We may repeat that the word "undifferentiated" as applied to 

 a germ means that it is not as a whole specialised for the performance 

 of any function within an organism, and has therefore the power of 

 giving rise to energids of all the kinds found in the body. It does 



