RELATIONS OF OVA AND GEMM/E. 193 



viviparous Aphides, though they state that there are obvious 

 differences both in the form of the ovarium, and in some 

 collateral phenomena, such as the absence in the latter of 

 those intermediate clusters of cells commonly termed vitel- 

 ligenous, which are regarded by Dr. A. Thomson as a sort 

 of normally abortive ova, and are compared by Dr. Carpenter 

 to the sterile yolk segments, which form so peculiar a feature 

 in the development of some Gasteropodous Mollusca.* 



The preponderance of testimony, therefore, is decidedly 

 in favour of the germs of the viviparous Aphides having 

 essentially the structure of ova. 



The same is maintained by Leuckart of the " eggs" of 

 some Coccida, which, though not impregnated, are found 

 to contain embryos, immediately on being laid. The re- 

 production of Coccida has also been examined by Mr. Lub- 

 bock, who arrives at the same conclusion namely, that 

 there is absolutely nothing, so far as our knowledge at pre- 

 sent extends, to distinguish the egg formation, from that 

 which occurs in any other Hemipterous insect, f 



It appears, too, from the recent observations of Leuckart, 

 that in the genus Chermes, which is also gemmiparous, and 

 is intermediate in some degree between the two families 

 just referred to, all the parts concerned in the formation 

 and development of true ova are more or less represented, 

 for the germ, which contains a very distinct vesicle, lies in 

 an ovary of the usual type, and furnished with appendages 

 resembling the accessory glands and spermatheca of ordi- 

 nary female^ insects.! 



3. All this must incline us, as the author just quoted 



* Huxley, in Annals of Nat. Hist., 3d Ser., II., 215. Lubbock on the 

 Ova of Insects, Op. Cit., III., 499 ; and Philosoph. Transact., Nov. 1858. 

 Thomson, in Cyclop, of Anat. and Physiol. (Ovum) . 



f Philosoph. Transact., Dec., 1858. 



J Annals of Nat. History, 3d Ser., IV., 321-1-11, " on the Reproduction 

 of the Bark-lice." 



K 



