104 MISS EMBLETON ON CERATAPHIS LA.TANIJ1]. 



successive, in correspondence "with external co-existences and 

 sequences." A biological individual is therefore one which 

 possesses the power to live alone, given suitable conditions, and 

 which is a wholly or partially independent organized mass, 

 arising continuously or discontinuously : " we must accord the 

 title to each separate aphis, each polype of a polypedom . . . . " 

 There are anomalies, which he regards as inevitable, if the 

 hvpothesis of Evolution is correct, for organic forms must have 

 arisen, by insensible gradations; but he concludes the chapter 

 by saying : " We must be content with a course which commits 

 us to the smallest number of incongruities ; and this course is, 

 to consider as an individual, any organized mass [centre or 

 axis] * that is capable of independently carrying on that 

 continuous adjustment of inner to outer relations w^hich 

 constitutes Life." 



Since the period at which Huxley and Spencer wrote, our 

 knowledge of the cycles of generations in ApJiidce has become 

 more extended, and the life-hi stories have been found in many 

 eases to be extretnely complex. As has been stated above, in 

 the case of Ceratapliis latanice in this country, the species is 

 apparently maintained permanently by parthenogenetic psedo- 

 genesis of an aleurodiform instar. According to Huxley's view, 

 we must consider all the specimens co-existent in different parts 

 of this country, and those of all past generations that have 

 presented the same phenomena, as a single individual. 



It is well known to modern zoologists that there exists a 

 great variety of individuals, individualities, and individual 

 lives ; and Spencer's definition is clearly more convenient 

 practically than Huxley's, though it conveys no connotation of 

 this variety. 



The permanent, or quasi-permanent, condition of CeratapMs 

 latanicB in this country lends additional support to the view, at 

 pr. sent accepted very widely, that in polymorphic insiects the 

 particular form attained by an individual is determined by the 

 food. In SurmapMs Jiamamelidis the form is altered when the 

 food becomes inadequate, and recourse is had to living on 

 the leaves of another tree. On this the aleurodiform generations 

 are maintained till the nutriment fails in the autumn, when 

 winged forms are again produced. As the conditions under 



* Omitted in 1S98 edition. 



