ASSOCIATION OF CHROMOSOMES IN DIPTEBA 219 



Preparations have been made from gonads of both sexes, 

 and somatic tissues of various kinds. Almost all of the latter 

 represent embryonic staged, including eggs, larvae and pupae. 

 The former have been taken from larvae, pupae or adults, or 

 all three, depending upon the species. In some species all 

 stages from early spermatogonia or oogonia to the formation 

 of spermatozoa or eggs could be secured from adults, but in 

 most cases it was necessary to use pupae or even larvae in order 

 to obtain the desired stages. This is especially true of the 

 family Drosophilidae. In all cases the gonads or small hits of 

 tissue were dissected out of the specimens and then fixed; none of 

 the specimens was fixed entire or partially intact. This fact 

 is emphasized because it has been found that regardless of the 

 fixative used, inferior results are obtained if tissues are fixed 

 in situ. 



Dissections were usually made in Ringer's solution except in 

 the case of large specimens, when tissues were dissected out 

 in the body fluid. Dissection in tap water was tried with fairly 

 good results, but mitotic figures were less distinct after this treat- 

 ment than after the use of Ringer's solution. ^ 



For fixation Flemming's strong solution was found most 

 satisfactory and was most frequently employed. Objects were 

 fixed from ten minutes to three hours depending upon their 

 size. Longer treatment was tried, but with less satisfactory 

 results due to frequent osmication and distortion. In addition 

 to Flemming's fluid various other fixatives were tried. Of these 

 Hermann's platino-aceto-osmic, and Gilson's mercuric-nitric 

 gave the best results (in many cases as favorable results as 

 those obtained by the use of Flemming's fluid), especially when 

 it was desirable to differentiate the chromosomes without refer- 

 ence to other nuclear structures. Sublimate acetic and Gilson- 

 Carnoy's acetic alcohol with sublimate were found fairly satis- 

 factory for somatic tissues, but were inferior for the gonads. 

 Bouin's fluid (formol mixture) though frequently used, proved 

 quite undesirable because of its tendency to distort and produce 



- Dissection in tap water has been recommended by Doncaster ('14) for 

 Abraxis. 



