STATE HORTICULTURAL SOCIETY. 151 



sprang, and they, in turn, produce a similar brood in the same anomalous 

 manner. This process is repeated again and again during the summer 

 and until in the fall, through some six or seven, or even more gener- 

 ations. The last fall brood presents a remarkable change, for it usually 

 consists almost entirely of males and females which acquire wings. These 

 winged females, as previously stated, after pairing, deposit eggs which 

 remain over the winter. 



It was formerly supposed that this fall brood consisted entirely of 

 normal males and females, but careful investigation shows this to be a 

 mistake, as there are usually a number of the agamic females among them, 

 showing a tendency to continue the anomalous method of reproduction, 

 which is apparently checked by the approach of the cold season. It has 

 been found possible, by placing the agamic females of the summer brood 

 in a situation of uniform and sufficiently warm temperature, to cause the 

 viviparous generation to go on indefinitely. I have even observed it 

 going on in the middle of winter, in specimens of the Wheat Plant-louse 

 {Aphis avence), taken from the wheat while snow was on the ground. 

 Instances are on record of this method of generation continuing for four 

 years without interruption. 



It is proper to remark that there are some species in which the agamic 

 females do not produce living young, but eggs — the reproduction, in 

 other respects, being similar to that described. It is also a singular fact 

 that there is an intermediate group, in which the young larvae are brought 

 forth in a very thin and delicate egg-like sack. 



How is this mode of reproduction to be explained ? is a question 

 that has troubled naturalists from the day of Bonnet, who first discovered 

 it, down to the present time. Leuroenhoek and Cestoni were of the 

 opinion that the supposed agamic females were in fact hermaphrodites. 

 Morren, a professor of the University of Liege, after a careful anatomical 

 examination, apparently set this theory at rest. It was his opinion — a 

 view adopted by the celebrated Owen — that all these changes are brought 

 about by some force concentrated in the sperm cells, or, as the latter has, 

 in substance, expressed it, the spermatic force is transmitted to a mass of 

 germ cells, and these germ cells are the direct excitants of all the changes 

 in the successive generation of cells, until the impregnation of the next 

 ovum. On this theory, the germ stock — for " force," as here used, can 

 mean nothing else — would soon be exhausted, and the reproduction 

 limited. It also requires the transmission of a part of the original germ 

 stock through, sometimes, as many as twenty generations, and with a 

 possible division, according to Owen himself, among more than a million 

 times a hundred million descendants. Another serious objection to this 

 theory is the evidence furnished by Kyber's experiment, in which he kept 

 up viviparous generation for four years, at the end of which the agamic 

 females appeared to have the same power of reproduction as the first 

 brood. I do not fiilly and clearly understand Huxley's theory, but the 

 chief idea appears to be that of germination or budding, somewhat simi- 

 lar to that observed in some of the Polypi. But his explanation of the 

 production of the ovum in the fall is scarcely satisfactory. Dr. Burnett, 



