SOMATIC MITOSES OF THE MOSQUITO 581 



cc. 



Picric acid saturated 75 



Formalin 15 



Glacial Acetic acid 10 



Flemming's solution gave much the more accurate results 

 particularly on the earlier stages. For perfect fixation with this 

 fluid, however, the larvae must be teased finely in the solution 

 or else the chitinous covering will prevent penetration. P. F. A. 

 No 3 gives excellent results on the metaphase chromosomes but 

 the early stages of the chromosomes are very likely to be wholly 

 or partially fused, giving a totally erroneous impression of the 

 actual conditions. When larvae were fixed in this killing fluid 

 the head and thorax were severed from the abdomen and before 

 placing in the warm fluid. Smears of the thorax were made and 

 fixed in Flemming's solution but although thirty animals were 

 prepared in this way no division figures were found. The gen- 

 eral fixation was very good. 



The material was dehydrated by allowing 95 per cent alcohol 

 to displace the killing fluid drop by drop, until the fixative was 

 entirely eliminated and the tissue stood in 95 per cent alcohol. 

 When Flemming was used the material was first washed in 

 water and then dehydrated in the same way. It was found 

 unnecessary to remove the picric acid completely, as is usually 

 advised following a picric acid fixative. The tissue fixed in 

 P. F. A. Xo. 3 was cleared in aniline oil and the Flemming mate- 

 rial was cleared in cedar oil. Either of these oils was followed 

 with xylol, imbedded in paraffin and cut in sections six micra 

 thick. In imbedding a number of thoraces or bodies the pieces 

 were oriented one behind the other, which simplified the cutting 

 materially (Hance, '15). When finely teased tissue was being 

 prepared for cutting, the material in xylol was poured into a 

 paper box or boat and the xylol was drained off through the 

 paper, leaving the tissue massed at one end of the boat. The 

 paraffin was poured into this paper form and the box was placed 

 in melted paraffin. In this way it was easy to retain the finely 

 divided tissue. Iron alum-haematoxylin was used exclusively in 

 staining. 



