;J44 INSECTA. 



bryonic formation, and a larval individual (fig. 172, 3, e) like that from 

 the ovum is thus produced, which is only not retained in connexion 

 with its parent because the abdominal integument is not co-extended 

 with it. 



(900.) The generation of a larval Aphis may be repeated from seven 

 to eleven times without any more accession to the primary spermatic 

 virtue of the retained germ-masses than in the case of the zoophyte or 

 plant : one might call the generation an " internal gemmation ; " but 

 this phrase would not explain the conditions essential to the process, 

 unless we previously knew those conditions in regard to ordinary or 

 external gemmation. At length, however, the last apterous or larval 

 Aphis so developed proceeds to be metamorphosed, as it is termed, into 

 a winged individual, in which, only, the fertilizing filaments are formed, 

 as in the case of the stamens of the plant (7i) another larval Aphis 

 (fig. 172, 3, i) perfects the female generative organs, and developes the 

 ovules, as in the case of the pistil (fig. 172, 1, i). We have, in fact, at 

 length male (h) and female (i) individuals, preceded by reproductive 

 individuals (e e) of a lower or arrested grade of organization, analogous 

 to the gemmiparous polyps of the zoophytes (fig. 172, 2, e e) and the 

 leaves (fig. 172, 1, e e) of the plant. 



(901.) The process of development in the Aphides is, for its better 

 intelligibility, described above by Professor Owen as one of a simple suc- 

 cession 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 broods ; and each of these larvae repeats the pro- 

 cess ; and it may be again repeated in the same geometrical ratio, until 

 a number which figures only can indicate, and which language almost 

 fails to express, is the result. The Aphides, generated from virgin 

 parents by this process of internal gemmation, are as countless as the 

 leaves of a tree to which they are so closely analogous. The wingless 

 larval Aphides are not very locomotive ; they might have been attached 

 to one another by continuity of integument, and each have been fixed 

 to suck the juices from the part of the plant where it was brought forth. 

 The stem of the rose might have been incrusted with a chain of such 

 connected larvae, as we see the stem of a fucus incrusted with a chain 

 of connecting polyps, and only the last developed winged males and 

 oviparous females might have been set free. The connecting medium 

 might even have permitted a common current of nutriment, contributed 

 to by each individual, to circulate through the whole compound body. 

 But how little of anything essential to the animal would be affected by 

 cutting through this hypothetical connecting and vascular integument, 

 and setting each individual free ! * 



(902.) In all the great class of Insects, the blood is equably diffused 

 through the visceral cavity, and is -contained in the spaces intervening 



* Loc. cit. p. 61. 



