26O C. W. METZ. 



observed such loop structures in any other Diptera. This gives 

 some ground for expecting similar synaptic phenomena in the two 

 sexes in regard to the feature with which we are concerned here. 

 After the growth period is well under way and the oocytes are 

 clearly differentiated from the other cells, the chromatin appears in 

 the form of large, irregular, heavily granulated aggregates whose 

 structure I am unable to analyze. Before this, however, there 

 appears to be a diffuse stage in which scarcely any chromatin is 

 visible in the nucleus. My present material is not adequate for a 

 detailed study of these stages and their treatment must be deferred. 



DISCUSSION. 



The above facts, it is believed, provide strong support for the 

 conclusion that, in the male Dasyllis at least, synapsis is not uni- 

 form throughout the length of the chromosomes, but may, in the 

 case of certain chromosomes, occur only in the terminal regions, 

 leaving the homologous members separated near the middle. 



So far as I know, no equally clear cases of this sort have been 

 described before, although figures that suggest a similar condition 

 are given by Mohr ('16, Figs. 85-90) for Locusta vwidissima, 

 by Robertson ('16, Fig. 163) for Chortippus curtipennis? and by 

 Wenrich ('16, Figs. 73-78) for Phrynotettix magnus. These are 

 interpreted by the authors as cases of delayed synapsis (Locusta 

 and Phrynotettix} , or early separation of threads after synapsis 

 (Chortippus) ; but it is possible that with further study some of 

 them may prove to be cases of incomplete synapsis. Professor 

 McClung informs me that similar conditions may exist in other 

 Orthoptera on which he has made preliminary observations. 



It has also been suggested to me by McClung that the absence 

 of synapsis in the median part of the long J- and V-shaped chromo- 

 somes in Dasyllis may be due to these chromosomes each being 

 compounded of two rod-like chromosomes united end to end, as 

 he has found chromosomes to be united in Hesperotettix (Mc- 

 Clung, '17). This offers an attractive lead toward an explanation, 

 but it is necessary to assume some other influence as well, else all 

 compound chromosomes should show this behavior. The latter 



2 1 am indebted to Prof. E. B. Wilson for calling my attention to the 

 former, and to Prof. C. E. McClung for calling my attention to the latter case. 



