CHROMOSOMES OF MOSQUITO 557 



This approximation of homologues in diploid cells is evidently 

 something very different from synapsis in the true sense, which 

 is restricted to the first gametocyte. In the former case there 

 is no reduction in number of the chromosomes which appear 

 for the next mitosis. In the latter case we have pseudoreduction 

 which persists until they are separated either by the first or by 

 the second maturation division. This was expressed by Stevens 

 ('08 p. 373) who, however, uses the term synapsis for pairing in 

 diploid cells. "In the spermatocyte we get complete synapsis 

 and reduction; in the spermatogonium, only a foreshadowing of 

 reduction, and abundant proof that synapsis is here a side-to- 

 side pairing of homologous chromosomes*.'' 



I would suggest therefore that the term synapsis be retained 

 for the uniting of the homologues in the first gametocyte, and 

 that approximations or brief temporary unions in diploid cells 

 be called 'pseudosynapsis.' The fundamental difference between 

 pseudosynapsis and synapsis is that the former results in no 

 permanent reduction, while the latter results in not merely a 

 pseudoreduction, a reduction in number, but ultimately in a 

 qualitative reduction, a separation of parental elements, which 

 may not take place until the second maturation division. 



The term 'synaptic phase' was employed by Moore to denote 

 the rest of transformation. The conditions have now been more 

 closely analysed (Wenrich, '16) and it is shown that the uniting 

 of the chromosomes, synapsis, takes place at the zygotene stage 

 and that the homologues are not permanently separated in some 

 cases until the second maturation division. I therefore use the 

 term 'synaptic condition' for the paired condition of the homo- 

 logues, which, in most forms, extends from the time of synapsis 

 in the zygotene stage to the final separation of the homologues 

 in the anaphase of the first or the second maturation division. 

 We have seen that in the Diptera a synaptic condition occurs in 

 diploid cells also, but that this is not brought about by a true 

 synapsis, since it results in no permanent numerical or qualita- 

 tive reduction. 



It is while the homologues are in the synaptic condition that 

 the closest union of parental elements takes place and this seems 



JOURNAL OF MORPHOLOGY, VOL. 28, NO. 2 



