Division in the Radiata. 397 



there are nevertheless many other cases in which it by no means 

 presents this character, but, as expressed by the term, is a 

 division and nothing else. In some cases (in the Asterida and 

 Ophiurida above mentioned, and perhaps in certain Actiniae) 

 this division is probably a normal form of increase which 

 replaces gemmation ; in others, on the contrary, it appears to 

 be quite accidental. On the one side, therefore, it is related 

 to regeneration, on the other to gemmation. Although it is 

 not always possible to indicate clearly the limit between these 

 phenomena, and division and gemmation often replace each 

 other, this does not prevent our retaining for " schizogony " 

 an independent place in the series of modes of agamic multi- 

 plication (monogony), side by side with internal and external 

 gemmation (blastogony), and with multiplication by free germs 

 (sporogony) or by unfecundated ova (parthenogony ) , especially 

 as it is a deduction from the scientific value and importance 

 of these categories that it seems to be difficult or even im- 

 possible to trace a marked line of separation between these 

 modes of multiplication, or between parthenogony and sexual 

 reproduction. But, as I have indicated above, the classification 

 in the category of schizogony of the phenomena of multiplica- 

 tion already described in the Asterida and Ophiurida has 

 precisely the effect of clearly establishing that spontaneous 

 division differs qualitatively from gemmation, which might 

 well have been regarded as doubtful so long as we had exclu- 

 sively or chiefly in view the phenomena presented by the 

 Coralliaria and Actiniae. 



The general propositions which sum up the present state of 

 our knowledge regarding spontaneous division may therefore, 

 I think, be provisionally enunciated as follows : — 



1. The most energetic manifestation of the faculty of re- 

 generation in animals is divisibility. 



2. In certain forms of Radiata in which the faculty of re- 

 generation is highly developed, spontaneous division occurs 

 either alone (Asterida and Ophiurida) or associated with gem- 

 mation (Actinige). 



3. True spontaneous division, or schizogony^ in the Actinige, 

 Medusa, Asterida, and Ophiurida (which must not be con- 

 founded with the disguised gemmation of the Infusoria, of 

 Scyjyhistoma, and of certain Chastopods) must be regarded as 

 a peculiar form of agamic reproduction, side by side with 

 blastogony, sporogony, and parthenogony. 



Ann. & Maq. N. H. Ser. 4. Vol. xii. 27 



