and Embryogeny of the Aphides. 05 



have in a very different manner in the sequel of the develop- 

 ment : that which has given origin to the female elements dis- 

 appears immediately afterwards, whilst the vesicle which has 

 generated theTnale or spermatic elements, far from disappearing, 

 continues its development, often becomes very large, and after 

 forming connexions with the female generative apparatus, con- 

 stitutes a reservoir for the fecundative corpuscles — becoming, in 

 fact, a true seminal vesicle for this hermaphrodite apparatus. 



When the curious phenomena just described summarily have 

 terminated, the embryonic development, properly so-called, has 

 not yet commenced. We may, indeed, observe that the cells of the 

 blastoderm have multiplied at the anterior pole so as to produce a 

 very considerable thickening there; but this modification is not fol- 

 lowed by the formation of any new part. This thicker layer, in 

 fact, soon gradually diminishes, and is at last entirely effaced*. 



XIII. — On the Reproduction and Embryogeny of the Aphides. 

 By M. Balbiani. (Second Note.)t 



In the viviparous Aphides the blastoderm assists to a certain 

 extent in the formation of the embryo, but its part is exclusively 

 limited to the production of the laminae which complete the ce- 

 phalic extremity in front. All the rest, on the contrary, results 

 from an entirely new part superadded to the blastoderm. 



The first phenomenon which denotes the commencement of 

 embryonic development is a budding forth of cells upon one of 

 the halves of the circumference of the aperture (of which I have 

 already indicated the purpose and mode of formation) at the 

 posterior pole of the blastoderm. The result of this budding is 

 the production of a cellular lamina, which gradually rises from 

 the margin of the preceding aperture into the interior of the 

 ovum, folding back against the inner wall of the blastoderm, 

 which it appears in some degree to double for a certain extent. 

 When arrived within a short distance of the anterior pole, it folds 

 inwards, inversely to its former direction, as if to descend again 

 towards the aperture which was its point of departure, but with- 

 out passiug, at least at this time, the middle of the ascending 



periods of embryonic development and even after birth, has been described 

 sometimes as serving for the nutrition of the embryo {pseudo-vitellus of 

 Huxley), sometimes as a plastic mass destined for the formation of the 

 vegetative organs (Leydig). 



* This transitory production of the blastoderm of the Aphides is pro- 

 bably the analogue of the " primitive cumulus " described by Claparede as 

 preceding the formation of the embryonal rudiment in the ova of the 

 Spiders. 



t Translated from the 'Comptes Rendus,' June llth, 1866, pp. 1286- 

 1289. 



Ann. 6^ Mag. N. Hist, Ser. 3. Vol. xviii. 5 



