Dr. Burnett on the Development of Viviparous Aphides. 95 



erroneous. I think, therefore, that the doctrine of Steenstrup 

 may prove to be unfounded as far as it would involve, intrinsically, 

 new phenomena in the processes of reproduction ; and, as I have 

 said on a preceding page, all its conditions may find their illus- 

 tration and solution in the various phases of gemmiparity*. 



If in this discussion of some of the highest relations of physio- 

 logy, we have not wandered too far from our subject proper which 

 we have thereby sought to illustrate indirectly, we will revert to 

 the thread of its discourse for a few concluding remarks. 



The final question now is, what is the legitimate interpretation 

 to be put upon the reproductive phenomena of the Aphides we 

 have described? My answer to this has been anticipated in the 

 foregoing remarks. I regard the whole as constituting only a 

 rather anomalous form of gemmiparity. As already shown, the 

 viviparous Aphides are sexless; they are not females, for they 

 have no proper female organs, no ovaries and oviducts. These 

 viviparous individuals therefore are simply gemmiparous, and 

 the budding is here internal instead of external as in the Polyps 

 and Acalephs ; it moreover takes on some of the morphological 

 peculiarities of oviparity ; but all these dissimilar conditions are 

 (Economical and extrinsic, and do not touch the intrinsic nature 

 of the processes concerned therein. 



Viewed in this way, the different broods of Aphides cannot 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 the other hand, the whole suite from the first to the 

 last constitute but a single true generation. I would insist upon 

 this point as illustrative of the distinction to be drawn between 

 sexual and gemmijmrous reproduction. Morphologically, they 

 have, it is true, many points of close resemblance ; but there is a 

 grand physiological difference, the true perception of which is 

 deeply connected with our highest appreciation of individual ani- 

 mal lifef. A true generation must be regarded as resulting only 

 from the conjugation of two opposite sexes— from a sexual pro- 



* This statement is made perhaps more strongly and exclusively than the 

 present state of our knowledge would warrant, but I throw it out much in 

 a suggestive way. There is no subject in physiology more interesting and 

 comprehensive than that of Gemmation ; the important question nowis, — 

 does it, as an individual process, embrace all the categories of plucnoinena 

 treated by Loven, Steenstrup, &c, these phenomena varying extrinsically, 

 according to (economical conditions, or do they (the phenomena) imply 

 something beyond and dissimilar from gemmation ? 



t In this view, as well as in several others herein discussed, I am pleased 

 to say that I have the support of so learned a physiologist as Dr. Carpenter. 

 See his Review " On the Development and Metamorphoses of Zoophvtes," 

 m the Brit, and Foreign Med. Chir. Rev. 1848, i. p. 183; and "On Repro- 

 duction and Repair," in ibid. 1849, ii. p. 419. 



