52 BRITISH APHIDES. 



into the tracheae of the live insects within ; I believe 

 this expansion is never to be noticed with reference to 

 the true ova. M. Lichtenstein has well distinguished 

 between these separate ovoid bodies, so like each 

 other, and yet so different in their destinations. 



Notwithstanding that objections have been taken to 

 the names proposed by Huxley for these two bodies, 

 I think the terms of ova and pseudova (false ova), 

 ovaria and pseudovaria, are very convenient ; and quite 

 as intelligible as buds and gemmae. 



But, after all, the phenomenon of viviparism may be 

 looked at as a process in which the completed foetal 

 development is effected within the parent, whilst in 

 oviparism that same process is deferred for some con- 

 siderable time, and in part is conducted externally to 

 the parent. 



From this point of view we might regard the whole 

 family Aphidida) (Ohermes and Phylloxera included) as 

 to their pseudova viviparous, but as to their real eggs 

 oviparous ; the difference only being that in the genera 

 of low grade the viviparous broods do not throw off 

 their membranes until after their birth.* These mem- 

 branes of the pseudova probably have no analogy to 

 the chorion of the true egg t but may be regarded as 

 mere sacs which enclose the embryos. 



Phylloxera vastatrix, Planchon. 



So much has been written on the vine Aphis, that it 

 will be well to offer here only a short summary of the 

 subject. For greater detail the reader is referred to 

 numerous memoirs found in the 'Comptes Rendus,' 

 1 Annals Soc. Ent. de France,' and other sources, the 

 chief of which are indicated in the bibliographical list at 

 the end of this present volume. 



Phylloxera vastatrix offers a good example of the 



* Vide vol. ii, p. 70, PI. lviii ; also vol. iii, pp. 98, 118, PI. cviii, and 

 PI. cxi, of this Monograph. 





