THE LAW OF EVOLUTION 



the development of the higher crustaceans, the 

 parallel chains of ganglia, which constitute the 



soon to form a second segment, which, instead of separating 

 as a new individual, remains partially attached to the first. 

 This process may go on until hundreds of segments have been 

 formed. Not only, moreover, does spontaneous fission occur 

 in nearly all the orders of the annul ose sub-kingdom, but it is 

 a familiar fact that artificial fission often results in the formation 

 of two or more independent animals. So self-sufficing are the 

 parts, that when the common earth-worm is cut in two, each 

 half continues its life as a perfect worm, — as is above ob- 

 served, in the text. Very significant, too, is the fact that in 

 some genera, as in chastogaster, where the perfect individual 

 consists of three segments, there is formed a fourth segment, 

 which breaks off from the rest and becomes a new animal. 



All these facts, together with many others of like implica- 

 tion, point to the conclusion that the type of annulosa has 

 arisen from the coalescence, in a linear series, of little sphe- 

 roidal animals primevally distinct from one another. How are 

 we to explain, or classify, such a coalescence ? May we not 

 most plausibly classify it as a case of arrested reproduction by 

 spontaneous fission ? In other words, whereas the aboriginal 

 annul oid had been in the habit of producing by gemmation a 

 second individual which separated itself at a certain stage of 

 growth, there came a time when such separation became ar- 

 rested before completion ; so that, instead of a series of inde- 

 pendent organisms, the result was a colony of organisms linked 

 together in a linear chain. Let us observe that by this brilliant 

 explanation the origin of the annulose type is completely assim- 

 ilated to the origin of the lowest animal and vegetal types. 

 The primordial type alike of the vegetable and of the animal 

 is a single spherical or spheroidal cell, which reproduces itself 

 by spontaneous fission. That is, it elongates until room is 

 made for a second nucleus, after which a notch appears in the 



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