312 T. H. MORGAN 



Tannreuther in 1907 studied the maturation of the partheno- 

 genetic and sexual eggs of the aphid, Melanoxanthus salicis. 

 He found the full number of chromosomes in the parthenogenetic 

 egg, and pointed out that no previous reduction stage was pre- 

 sent. His study of the earlier stages of this egg does not seem 

 to me to suffice to have precluded the possibility of a synapsis 

 stage being present, especially in the light of his wrong identifi- 

 cation of that stage in the sexual egg. Tannreuther missed the 

 reduction stage of the sexual egg, but describes at length a pro- 

 cess that he calls "reduction of chromosomes." This, he says, 

 occurs after the egg has left the ovary, but these stages can have 

 nothing to do with the synapsis for the pairing has already taken 

 place before this time. He also overlooked the synapsis stage in 

 the spermatogenesis; for, the pairing of the chromosomes which 

 he describes is a much later stage — probably a stage when the 

 reduced chromosomes are emerging for the first spermatocyte 

 division. The behavior of the lagging chromosome was wrongly 

 described and interpreted. My own observations relating to sy- 

 napsis in aphids and phylloxerans were published in 1910. 

 Gregoire in 1910 has given in an admirable resume an account 

 of what has been done in connection with synapsis and reduc- 

 tion in parthenogenetic eggs. In particular, he has drawn at- 

 tention to the similarities between the accounts of synapsis in 

 parthenogenetic eggs and apogamy in certain plants, where, ac- 

 cording to Strasburger, synapsis may occur, but fails to bring 

 about reduction in number of the chromosomes. In certain cases 

 Strasburger thinks that the figures show an attempt at reduction 

 at this time without union really taking place. 



The preceding evidence appears to show that a contraction 

 figure may appear that resembles synapsis as far as one may 

 judge from the general appearance alone, but which does not 

 lead to conjugation of the chromosomes. We have then the 

 alternatives of denying that here the contraction figure repre- 

 sents a true synapsis stage, or else of admitting that the contrac- 

 tion figure in itself is not a true criterion as to whether conjuga- 

 tion is taking place. There is also another possibility, namely, 

 that during the contraction phase conjugation of the chromo- 



