714 JOHN BEAED, 



220) may be cited. Haecker found and described under the name 

 of "Zwischenkerne" numerous germ-cells among the oocytes of Cantho- 

 camptus in degeneration. It is especially of interest to note, that 

 many of these obviously lie in the zone of sex-diiïereutitaion, where 

 the oogonia become oocytes. 



14. Where the parthenogenetic development of eggs of the one 

 sex, or of the other, has been initiated, there is an undoubted ten- 

 dency for such eggs to become in the long run incapable of fertili- 

 sation. This would appear to be so as a rule in the drone-eggs of 

 bees; but occasionally, as Dzierzon's experiments show^), and as 

 Weismann has recorded (op. cit. p. 495) of one instance in 272, some 

 drone-eggs may be fertilised 2). From the experiments of the former 

 it is clear, that such aberrant fertilisation is without influence on the 

 sex of the offspring; but, if the two parents be of different races, it 

 leads to "bastardism", i. e., crossing. 



15. Where parthenogenesis becomes cyclical (Weismann), as in 

 Apus, some Daphnidae, and Rotifera, and where thus the males tend 

 to disappear, this must simply be due to the constant and regular 

 suppression as such of the germ-cells, which ought to have produced 

 male-eggs, and from these males. Perhaps one might also hold, that 

 in those instances of the rare production of males, e. g., in Artemia 

 (Weismann Ishikawa)^), these had come under the influence of 

 panmixie. As Weismann has pointed out, they are useless organisms ; 



1) SiEBOLD, C. T. E. VON, Wahre Parthenogenesis bei Schmetter- 

 lingen und Bienen, I^eipzig 1856, p. 96. 



Compare section III, page 723. 



2) In his remarkable researches on the Daplmidae, already cited, 

 "Weismann has discussed the possibility of the fertilisation of the summer- 

 eggs (p. 324). "Por certain species at least copulation of the virgin- 

 females is impossible, because they lack the copulatory canal, which is 

 present in the sexual females of the like species. This condition obtains 

 in Bythotrephes, Evadne and Podon.^^ 



These cases appear to represent a stage further than that, in which 

 the fertilisation of the parthenogenetic egg has become impossible, for 

 here fertilisation is superseded by impotence on the part of the female. 

 The reader may be reminded, that the parthenogenetic females of Aphis 

 possess no receptaculum seminis. 



3) Wkismann, a., u. Ishikawa, C, Weitere Untersuchungen zum 

 Zahlengesetz der Richtungskörper, in: Zool. Jahrb., V. 3, Anat., 1888, 

 p. 579. 



