58 PROCEEDINGS OF THE AMERICAN ACADEMY 



teristics of these last, — such as a vitellus, a germinative vesicle, and 

 dot ; on the other hand, they are at first simple collections, in oval 

 masses, of nucleated cells. Then, again, they receive no special 

 fecundating power from the male, which is the necessary preliminary 

 condition of all true eggs ; and furthermore, the appearance of the 

 new individual is not preceded by the phenomena of segmentation, as 

 is also the case with all true eggs. Thferefore, their primitive forma- 

 tion, their development, and the preparatory changes they undergo for 

 the evolution of the new individual, are all different from those of real 

 ova. 



" Another point of equal importance is, these viviparous individuals 

 of the Aphides have no proper ovaries and oviducts. Distinct organs 

 of this kind I have never been able to make out. The germs, as we 

 have before seen, are situated in moniliform rows, like the successive 

 joints of confervoid plants, and are not inclosed in a special tube. 

 These rows of germs commence each from a single germ-mass, which 

 sprouts from the inner surface of the animal, and increases in length 

 and the number of its component parts by the successive formation of 

 new germs by the constriction process as already described. More- 

 over, these rows of germs, which, at one period, closely resemble in 

 general form the ovaries of some true Insecta, are not continuous 

 with any uterine or other female organ, and therefore do not at all 

 communicate with the external world ; on the other hand, they are 

 simply attached to the inner surface of the animal, and their compo- 

 nent germs are detached into the abdominal cavity as fast as they are 

 developed, and thence escape outwards through a porus genitalis. 



^' With these data, the question arises. What is the proper interpre- 

 tation to be put upon these reproductive phenomena we have just de- 

 scribed } My answer would be, that the whole constitutes only a 

 rather anomalous form of gemmiparity : as already shown, the vivip- 

 arous Aphididse are sexless ; they are not females, for they have no 

 female organs, they are simply genwiiparous, and the budding is in- 

 ternal, instead of external, as with the Polypi and Acalephse ; more- 

 over, this budding takes on Some of the morphological peculiarities of 

 oviparity, but these peculiarities are economical and extrinsic, and do 

 not touch the intrinsic nature of the processes therein concerned. 

 Viewed in this way, the different broods or colonies of Aphididae can- 

 not be said to constitute as many true generations, any more than the 

 different branches of a tree can be said to constitute as many trees ; on 



