PHYLLOXERA QUEECUS. 51 



No fewer than sixteen species of Phylloxera were 

 named in America in 1875.* M. Lichtenstein thinks 

 it safe to decide that only five well-defined species 

 inhabit France, viz. P. coccinea, Heyd.; P. cortical is, 

 P. quercus, P. punctata, and P. vastatrix. 



I have not yet been able with certainty to identify 

 more than the two last-named species as British 

 denizens, and of these the vine Phylloxera must be 

 regarded as a late introduction into these Islands. 



Although the pseud-ova of Aphides take their origin 

 from internal organs which morphologically cannot 

 be separated from the true ovaria, the former should 

 not be confounded with the true egg, which is always 

 compounded of a true yolk and a germinal vesicle. 

 Probably this egg would be wholly sterile without the 

 influence of the male Aphis. 



A slight examination of the abdominal contents of 

 any viviparous female of Aphis will show that all 

 stages of completeness obtain, from the minute 

 nucleated point in the ovary to the well-developed 

 young ready for birtb. These embryos are all included 

 in an ovoid chamber, a kind of follicle ; and in many 

 species the insects are excluded, still enshrouded in 

 glistening membranes which appear very like eggs. 



In early days it was often a subject for discussion 

 whether the product of an Aphis was not always an 

 egg, and there are several species of true Aphis which 

 deliver their young so much in the form of ova, that 

 they well might deceive the incautious observer. 



Examples of such are to be found figured in this 

 Monograph. Thus with Aphis petasiticlis, Schizoneura 

 ulmi, and Pemphigus bursarius, the young do not extri- 

 cate their limbs from their investments till some 

 minutes after birth. The curious growth of these 

 young from the pseudova which is sometimes seen, and 

 which is very rapid, is caused by the inspiration of air 



* Interesting information on the American Phylloxeras is to be 

 found in Prof. Riley's Seventh Report on Noxious Insects in Missouri, 

 p. 97, et seq. 



