466 



THE INSECTA. 



§855^. 



peculiarities are economical and extrinsic, and do 

 not touch the mtrinsic nature of the processes there- 

 in concerned. Tiewed in this way, the different 

 broods cr colonies of Aphididae cannot be said to 

 constitute as many true generations, any more than 

 the dilferent branches of a tree can be said to con- 

 stitute as many trees ; on the other hand the whole 

 suite, from the first to the last, constitute but a 

 single true generation. I would insist upon this 

 point as illustrative of the distinction to be drawn 

 between sexual and gemmiparous reproduction. 

 Morphologically, these two forms of reproduction, 

 have, it is true, many points of close resemblance, 

 but there is a grand physiological difference, the 

 perception of which is deeply connected with our 

 highest appreciation of individual animal life. 



A true generation must be regarded as resulting 

 only from the conjugation of two opposite sexes, — 

 from a sexual process in which the potential repre- 

 sentatives (spermatic particle and ovum) of two op- 

 posite sexes are united for the elimination of one 

 germ. The germ power thus formed may be ex- 

 tended by gemmation or fission, but it can be 

 formed only by the act of generation, and its play 

 of extension by budding or by division must always 

 be within a certain cycle, which cycle is recom- 

 menced by the new act of the conjugation again of 

 the two sexes. In this way the dignity of the 

 ovum as the primordium of all true individuality, 

 is maintained. 



I have thus treated this subject in some detail, 

 not only from its wide bearing in the physiology of 

 reproduction, but also from its direct relation to 

 many phenomena alluded to in the preceding 

 pages. In the memoir from which I have made 

 this extract (read before the Amer. Acad. Arts 

 tavX Sc., Oct. 11, 1SÖ3) I have eatered into a full 



discussion of those many points suggested by these 

 studies. One of these, is, the relation of this subject 

 to some of the various doctrines of development, 

 which have been advanced in late years, such as 

 that of Alternation of Generation^ by Steen- 

 strup, and that of Parthenogenesis by Owen. I 

 have there attempted to show that the phenomena 

 of these doctrines, as advanced by their respective 

 advocates, all belong to those of gemmiparity, and 

 that therefore Alternation of Generation and Par- 

 thenogenesis in their implied sense, are misno- 

 mers in physiology. Another point there treated 

 in extenso, is the identity of this mode of repro- 

 duction we have just described in the Aphididae, 

 with that observed in the so-called hibernating eggs 

 of the Entomostraca (see above, § 290) and the like 

 phenomena observed in nearly every class of the 

 Invertebrata. They are all referable, in my opinion, 

 to the conditions of gemmation, modified in each 

 particular case, perhaps, by the economical rela- 

 tions of the animal. 



See for some recent writings on this peculiar 

 form of reproduction with the Insecta, and which 

 contain many interesting physiological remarks, 

 Leydig, Die Dotterfurchung nach ihrem Vor- 

 kommen in der Thierwelt und nach ihrer Bedeu- 

 tung, in the Isis, ISiS, lift. 3 ; also, Einige Bemer- 

 kungen über die Entwickelung der Blattläuse, in 

 Siebold and Kölliker^s Zeitsch. II. 1850, p. 62 ; 

 also Zur Anatomie von Coccus hesperidum, in Ibid, 

 1853, V. p. 1 ; Victor Carus, Zur näheren Kennt- 

 niss des Generationswechsels, Leipsig, 1849 ; and 

 Siebold, as referred to in my note under § 348 note 

 4. I cannot here discuss the often similar and 

 dissimilar views to those of my own above detailed, 

 expressed by these different investigators. — E». 



