546 P. W. WHITING 



sected, but 'synizesis,' nevertheless, occurred. The fusion of 

 the chromosomes in the picro-formol-agetic material is seen in 

 figures 107, 108, 109, and 110. 



b. Review and criticism of literature 



It will now be of interest to consider the technique employed 

 by the different investigators in the study of the chromosomes 

 of Diptera. 



Stevens ('09) "removed the anterior segments and secured 

 good fixation in Flemming's fluid and fairly good in Gilson's 

 mercuro-nitric." Most of her work was done, however, with 

 aceto-carmine which tends to swell the tissue. The gonads 

 were dissected out for the aceto-carmine method. The errors 

 in Stevens' work are few and her results more consistent than 

 either Taylor's or Lomen's. 



Lomen ('14) simply cut the larvae, pupae, and adults in the 

 middle and fixed in from 8 to 9 parts corrosive sublimate, 3 to 

 4 parts absolute alcohol. To 96 parts of this were added 4 parts 

 of glacial acetic acid. This was called S-A-E. Zenker's po- 

 tassium-bichromate, sublmate, acetic, K-B-S-E, was also used 

 and was considered better for dividing figures. Lomen's figures 

 are all very diagrammatic. 



Taylor ('14) tried aceto-carmine for which she dissected out 

 the gonads. She states, however, that it is not permanent, not 

 good for finer details, nor for somatic mitoses. For material 

 to be sectioned she used as fixatives, Benda's fluid, acetic-bichro- 

 mate, Gilson's mercuro-nitric, Flemming, and Gilson-Petrunke- 

 witch. She does not state whether she dissected her material 

 to be sectioned, but since she laid such stress on somatic mitoses, 

 it is probable that she kept her tissue largely intact. Her figures 

 are consistent with each other neither in number of chromosomes 

 nor in their form. They suggest very careful drawings of poorly 

 fixed material. 



Metz ('14) has made use of aceto-carmine preparations and 

 Flemming material. In all cases the gonads were dissected out 

 before fixation. The chromosomes stand out clearly and are 



