GENERATION OF INSECTS. 413 



The condition which renders this seemingly strange and mysterious 

 generation of an embryo without precedent coitus possible, is the 

 retention of a portion of the cells of the germ-mass unchanged. One 

 sees such portion of the germ-mass taken into the semi-transparent 

 body of the embryo Aphis, like the remnant of the yelk in the chick. 

 I at first thought that it was about to be enclosed within the alimen- 

 tary canal ; but it is not so. As the embryo grows it assumes the 

 position of the ovarium, and becomes connected with, or aids in 

 forming the filamentary extremities of the eight oviducts. Individual 

 development is checked and arrested at the apterous larval condition. 

 It is plain, therefore, that the essential condition of the development 

 of another embryo in this larva is the retention of part of the progeny 

 of the primary impregnated germ-ceU. All gemmation, external or 

 internal, is essentially the same process ; but we should learn nothing 

 by being told that the virgin procreation of the Aphis was a process 

 of internal gemmation *, unless it were shown how that was connected 

 with the primitive mode of diffusion of the fertilising force through 

 the germ-mass ; in other words, unless the signification of the 

 "cleavage-process" of the impregnated egg had first been appre- 

 ciated, and the resemblance of its product to the basis of the bud • 

 been duly recognised. 



The production of a larval Aphis may be repeated from seven to 

 eleven times in as many successive virgin generations, without any 

 more accession to the primary spermatic virtue of the retained cells 

 than in the case of the successive development of polypes in the 

 compound zoophyte, or the successive budding of the individual 

 leaves in the equally compound plant. 



At length, however, the last apterous or larval Aphis, so developed, 

 proceeds to be " metamorphosed," as it is termed, either into a winged 

 individual, in which only the fertilising filaments are formed, as in 

 the case of the stamens of the plant ; or, it perfects the female 

 generative organs, and developes the ovules, as in the case of the 

 pistil. Thus there become "male and female individuals," pre- 

 ceded by procreative individuals of a lower or arrested grade of 

 organisation, analogous to the gemmiparous polypes of the zoophyte 

 and the leaves of the plant. 



The process has been described for its better intelligibility in the 

 Aphides as one of a simple succession of single individuals, but it is 

 much more marvellous in nature. The first-formed larva of early 

 spring procreates not one but eight larvae like itself in successive 



* Veiy good observations are, nevertheless, contained in CCLXVIII. 



