SEX IN APHIS. 143 



abdominal rings, four on the seventh, and none on 

 the remaining rings. The development of these wax 

 organs on the backs and sides are said to be correlated 

 with the abortion of the nectaries ; yet, as the honey- 

 tubes never exceed two in number, the above relation 

 is not clear. 



The reader is referred to this memoir for the 

 author's views as to the origin of the setae of the pro- 

 boscis and their relation to the rudiments of the man- 

 dibles and maxillae. These points have been generally 

 discussed by others in the case of Hemiptera. Like 

 myself, M. Witlaczil was unable to make out the walls 

 of a dorsal vessel. I have, however, repeatedly noted 

 in some transparent species an alternating and pul- 

 sating action down the dorsal regions. 



Germinal vesicles were, on many occasions, distinctly 

 visible to M. Witlaczil, and he states that the formation 

 of the blastoderm proceeds from behind forwards, and 

 that the cleavage is essentially equal. 



In adverting to the questions on Phylogeny, glanced 

 at in the Introduction to my third volume, and touched 

 upon at page 134, &c, of this volume, it must be con- 

 fessed that the details now offered are more of a 

 suggestive than a conclusive character. The high 

 antiquity of the family Aphididae, and the fact that 

 the fossil forms very closely resemble those of recent 

 genera, render it difficult to indicate with any sureness 

 the passage of Aphis out of any lower type of Insect. 



The general reader, perhaps, will agree that in a 

 monograph which is chiefly systematic, so large a 

 subject as Reproductive phenomena should be but 

 lightly touched upon. In the meagre sketch now 

 offered I have freely used the writings of Profs. 

 Huxley and Balfour. When I employ almost their 

 identical words, it is from the feeling that any attempt 

 on my part to recast them would be a loss to the 

 reader, 



