288 PROCEEDINGS OF THE ACADEMY OF [May, 



Dissecting under fluids iu the ordinary manner is not satisfactory 

 because of the small size of the animals. McMurrich's (5) method 

 of placing the animal iu the killing fluid, and with a needle in each 

 end pulling him asunder; or that employed^by Conklin (4) of first 

 removiug the head, and then pulling out the intestine by catching 

 the tail segment with a pair of forceps, is much more rapid. In 

 either case the intestine breaks at the junction of the anterior por- 

 tion, or stomach, with the middle portion, or " mid-gut." For 

 obtaining the intestine and the glands with their connection pre- 

 served, the posterior one or two segments are cut off with scissors 

 and the organs removed by pulling on the one or two anterior seg- 

 ments with forceps. The whole mass is easily handled, and the 

 normal relation is preserved through all the fluids. I have usually 

 dis.sected off the harder chitinous parts of the head iu oil just 

 before embedding. 



It has been necessary to give special attention to the means and 

 methods of fixation. As will appear more clearly later, the form 

 and relation of the cellular constituents depend upon the direction 

 of penetration of the killing fluid, as well as upon the strength of 

 the fluid employed. By the usual method of plunging the organs 

 directly into the killing fluid the penetration is, of course, from the 

 coelomic toward the luminal side of the cell. For the purpose of 

 obtaining penetration from the luminal toward the coelomic side of 

 the intestinal cells an hypodermic syringe was filled with killing 

 fluid, and the needle, made blunt by turning back the point, was 

 inserted through the mouth into the anterior portion of the mid- 

 gut. Then the posterior segment having been cut off as before to 

 free the posterior attachment of the intestine, all the segments back 

 of the second thoracic were slipped off together by holding the 

 anterior end with one pair of forceps and pulling with another. In 

 a few cases I was able to obtain a fairly good injection by inserting 

 the needle after extracting the intestine; but since it always suffers 

 more or less from handling, and it is always difficult to insert a 

 needle into a collapsed intestine without tearing it, the former proved 

 the safer if the more cruel method. 



The following killing fluids have been used : a, ninety-five per 

 cent, alcohol; b, saturated aqueous solution of corrosive sublimate; 

 c, the same with addition of two per cent, acetic acid; d, picroaoetic 

 after Lee, and e, after Omklin; /, Zenker's fluid; g, picro -formal in ; 

 /(, formo-alcohol ; i, osmic acetic; j osmic-bichromate (Altmann's); 



