GROWTH AND ASEXUAL GENESIS. 445 



such segments were permanently united (§§ 205-7 and note 

 to § 207). Part of the evidence there assigned, is evidence to 

 be here repeated in illustration of the direct antagonism of 

 Growth and Asexual-Genesis. We saw how, among the 

 lower Annelids, the string of segments produced by gemma- 

 tion presently divides transversely into two strings; and 

 how, in some cases, this resolution of the elongating string 

 of segments into groups that are to form separate individuals, 

 goes on so actively that as many as six groups are found in 

 different stages of progress to ultimate independence — a fact 

 implying a high rate of fissiparous multiplication.* Then we 

 saw that, in the superior annulose types, distinguished in the 

 mass by including the larger species, fission does not occur. 

 The higher Annelids do not propagate in this way; there is 

 no known case of new individuals being so formed among 

 the Myriapoda; nor do the Crustaceans afford us a single 

 instance of this primordial mode of increase. It is, 



indeed, true that while articulate animals never multiply 

 a sexually after this simplest method, and while they are 

 characterized in the mass by the cessation of agamogenesis of 

 every kind, there nevertheless occur in a few of their small 

 species, those higher forms of agamogenesis known as parthe- 

 nogenesis and pseudo-parthenogenesis; and that by these 

 some of them multiply very rapidly. Hereafter we shall 

 find, in the interpretation of these anomalies, further support 

 for the general doctrine. 



To the above evidence has to be added that which the 

 Vertebrata present. This may be very briefly summed up. 

 On the one hand this class, whether looked at in the aggre- 

 gate or in its particular species, immensely exceeds all other 

 classes in the sizes of its individuals ; and on the other hand, 

 agamogenesis under any form is absolutely unknown in it. 

 If it be said that budding occurs among the Tunicata which, 



* It has since been shown that in Myrianida fasciata as many as 29 at- 

 tached groups exist. See Cambridge Natural History, Vol. II, Worms, Roti- 

 fers and Polyzoa, p. 280. 





