Dr. Burnett on the Development of Viviparous Aphides. 97 



that I suspect that this gemmiparous mode of reproduction will 

 be found to be far from uncommon among most of the Inverte- 

 brata, when our researches into the history of their development 

 shall have been more widely extended*. 



P.S. — I regret that I should not have seen until now, when 

 this paper is concluded, the important writings of Leydig on the 

 subject under discussion. In his article " Einige Bemerkungen 

 liber die Entwickelung der Blattlause," in Siebold and Kolliker's 

 Zeitschr. f. wiss. Zool. 1850, ii. p. 62, he speaks of his former 

 observations in the Isis, 1848, iii. p. 184. These I have not seen, 

 neither also a work to which he refers, of J. Victor Cams 

 (Zu naheren Kenntniss des Generationswechsels, Leipzig, 1849). 

 Leydig, in his criticism of Carus's views, expresses the opinion 

 that the development of the viviparous Aphides is, histologically, 

 like that of the Articulata in general. According to him, also, 

 the germ-bodies undergo processes corresponding to those of 

 impregnated eggs. These statements of Leydig, who is an ex- 

 cellent observer, have induced me recently to repeat my observa- 

 tions ; but this afforded the same results as before, viz. that the 

 germ-bodies out of which are developed the viviparous Aphides 

 have no true histological identity with eggs. 



P.S.f Since the publication of this paper, I have enjoyed the 

 opportunity of making this series of investigations more complete, 

 by an examination of the terminal or last brood which appears 

 at the end of autumn. 



This terminal brood has hitherto been considered, as far as I 

 am aware, to be composed exclusively of males and females, or, 

 in other words, of perfect insects of both sexes. I was surprised, 

 therefore, on examining the internal organs of the non-winged 

 individuals, to find that many of these last were not females 



* Notice may here be given of some curious observations, which Filippi 

 (Ann. Nat. Hist. ix. June 1852, p. 461) has furnished on the development of 

 the Pteromalidae. A Pteromalus lives in the ova of Rhynchltes betuleti ; 

 in each of these ova there is seen, soon after its deposit, a minute infusorial 

 animal, with a tail by which it moves briskly about among the vitelline 

 cells. It soon ceases to move, however, and in its interior appears a vesicle 

 which increases and changes into a larva which is that of Pteromalus ; this 

 larva becomes a pupa, and, after eight or ten days, changes to the perfect 

 insect which escapes from the ovum. If these observations are verified, we 

 have here a case exactly like that of the Aphides, excepting that, like the 

 Distoma, the intermediate budding form is very low, and takes on none of 

 the zoological peculiarities of the parent. But these statements need 

 corroboration, for they do not agree with the history of other species of 

 Pteromalus whose development is well known. See also the wonderful 

 gemmiparous phenomena related by Siebold of Gyrodactylus ; Siebold 

 and Kolliker's Zeitschr. f. wiss. Zool. i. 1849, p. 34/. 



t Silliman's Journal for March. 

 Ann. fy Mag. N. Hist. Ser. 2. Vol. xiv. 7 



