ZOOGENESIS 



In connection with this so-called asexual reproduc- 

 tion the extraordinary powers of regeneration pos- 

 sessed by certain types of animals deserves a special 

 mention. Some creatures may be cut into a great 

 number of small fragments, and each fragment will 

 subsequently grow into a perfect animal. In other 

 creatures fragments above a certain minimum size, or 

 including a greater or lesser portion of some essential 

 structure, will grow into a perfect animal. In still 

 other creatures division or mutilation of the body is 

 followed by the replacement, by the central portion, 

 of the parts removed. But the fragments not includ- 

 ing this central portion die. 



A curious form of reproduction is seen in certain 

 minute parasitic wasps in which a single egg gives 

 rise to from two or three to about a thousand larvas. 

 In somewhat the same way the egg of certain poly- 

 zoans develops into a multinucleated mass which 

 buds off small pieces, each of which becomes a 

 larva. 



To a large extent asexual reproduction is especially 

 characteristic of the early stages or the young of the 

 animal types wherein it occurs, the individuals which 

 are fully grown being capable only of sexual repro- 

 duction. Thus in certain brittle-stars very young in- 

 dividuals divide into two, and each half then grows 

 into an adult. Certain starfishes when young divide 

 themselves into five sections, the five arms, separating 

 at the base; subsequently each arm grows four more 

 arms, and the original single little starfish becomes 

 five adults. But in none of the brittle-stars or star- 



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