CHAPTER XVIII 

 THE STARFISH: A STUDY OF EMBRYOLOGY 



Since fatal accidents are all the time happening to individ- 

 uals of any species, in the course of time a species would become 

 entirely extinct were there not some way of continuing it. 

 All animals as well as plants have a single method of making 

 good the losses due to death, and this method is the division 

 of the individual, so that two or even a hundred or more 

 take the place of one. This process of multiphcation of indi- 

 viduals through the division of a single indi-vidual is called 

 reproduction. 



Although all forms of reproduction are fundamentally one, 

 several sorts maj^ be distinguished, owing to certain minor 

 differences between them. Thus there is the method of fis- 

 sion, as seen in the lowest organisms, in which the bod}' of the 

 reproducing individual divides into two equivalent parts. 

 Then there is reproduction by budding, as seen in certain 

 aquatic animals and nearly all plants, where an outgrowth or 

 bud arises on the side of the parent individual. This l)ud 

 gradually develops into the form of the adult and may then, 

 under certain circumstances, be cut off from the bodj' of the 

 parent indi\'idual. Also there is the method of sporulation, 

 in which the Irody of a single organism breaks up at once into 

 a large number of equivalent parts called spores. The method 

 that has become commonest among both animals and plants, 

 however, is that of reproduction by germ-cells. By this process 



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