564 W. L. TOWER, 



Methods. 



The material upon which this paper is based was preserved in 

 many ways, but none of the methods usually recommended for insect 

 tissues gave reliable results. Thus Perenyi's fluid used hot or cold, 

 Coriossive Sublimate, any Picric acid or Chromic acid mixture were 

 unsatisfactory. Hermann's fluid, Flemming's fluid and Corrosive 

 Sublimate acetic acid mixtures gave uniform and excellent results. 

 Hermann's and Flemming's fluids gave excellent results with small 

 pieces or young larvae, but were entirely unadapted to older or large 

 larvae or pupae. After much experimentation I have devised these 

 solutions of sublimate acetic acid which gave uniform results and 

 results that are exactly like those given by Hermann's or Flem- 

 ming's fluid : 



No. 1. 

 Saturated sol. HgCla in So^/q alcohol 

 Glacial acetic acid (99.5 "/(,) 

 Nitric acid "c. p." 



No. 2. 

 Saturated sol. HgC^ in 35 °/o alcohol 

 Glacial acetic acid (99.5 ^/q) 

 Nitric acid "c. p." 



No. 3. 

 Saturated sol. HgCljj in 35^0 alcohol 

 Glacial acetic acid (99.5 ^^/q) 

 Platinic chloride 2% sol. in Aq. dest. 



For large larvae or pupae I use No. 1, heated to 80° C in a 

 closed flask I poured suddenly over the specimens and allowed the 

 fluid to act for from two to five minutes according to the size of 

 the insect and the thickness of the chitin, then poured off and re- 

 placed by No. 2 and kept at a temperature of 30—40 " C for several 

 hours. Immediately after the removal from No. 1 the insect should 

 be cut with a sharp knife in as many pieces or places as possible. 

 By this method I have obtained a perfect fixation of the araoel)oid 

 processes of the intestinal epithelium of large Scarabaeid grubs when 

 fixed entire. For small larvae and pupae No. 1 is too strong and 

 should be replaced by No. 2 and used as in the case given above. 

 Perhaps the most generally useful is No. 3, which gives excellent 

 results either cold or warm but care should be taken to have as small 

 pieces of tissue as possible. 



