544 P. W. WHITING 



The gonads were fixed from two to twenty-four hours in small 

 vials. The fluid was then replaced by water in which the tissue 

 was left over-night. The water was then gradually replaced 

 with alcohol until the percentage reached 95, in which the tissue 

 was stained with eosin for the purpose of orientation in the 

 paraffin. Clearing was done in aniline oil followed by bergamot 

 or xylol and when all the water and alcohol were removed the 

 gonads were transferred from the vials to melted paraffin. About 

 one hour sufficed for thorough infiltration. Sections were cut 

 6^ in thickness and Heidenhain's iron-haematoxylin was used 

 with no counterstain. A few testes were dissected out and 

 fixed in Allen's picro-formol-acetic. This gave fair fixation but 

 the chromosomes appeared much shorter and thicker and had a 

 greater tendency to fuse. A few abdomens of adult females 

 were torn to pieces in Flemming's fluid and good fixation of 

 dividing figures was obtained. 



It was found to be difficult to obtain good penetration of 

 thoracic hypodermis. In the larvae this tissue is full of division 

 figures, but the chitinous epidermis, binding so closely on the 

 outside, and the adipose tissue, adhering on the inside, seem to 

 prevent the proper penetration. Probably the fat takes up the 

 osmic acid, as it appears much blackened. The attempt was 

 made to remove the epidermis, and although the outer layer 

 was removed, the inner layer still interfered considerably with 

 penetration. By considerable searching, however, it was possi- 

 ble to obtain a few good figures at the edge of the tissue. Mitoses 

 nearer the center were usually much distorted, and the chromo- 

 somes lying near each other were fused. 



All degrees of fusion were observed in the chromosomes, corre- 

 sponding to the distance of the cells from the cut edge of the 

 tissue. This fusion is very striking in picro-formol-acetic. 

 Often each pair appears like one chromosome, so that there 

 will be only three chromosomes instead of six. In tissue put 

 up in picro-formol-acetic without dissecting, spermatogonial pro- 

 metaphases often appear so distorted that they fuse into a tri- 

 angle, each corner of which corresponds to the approximated 

 ends of two pairs. The chromatin may then become aggregated 



