DEVELOPMENT OF PHRTGANIDS. 557 



sufficient. When it was necessary to cut sections of the 

 larvse, it was found of the utmost importance to transfer them 

 from absolute alcohol to benzole, and then into a solution 

 of benzole and paraffine in the manner described above. The 

 larvae invariably collapse when placed in clove oil or turpentine. 

 When they are to be mounted in toto the same principal can 

 be applied by mounting them in balsam dissolved in benzol ; 

 the solution which can be used thin at first may then be 

 allowed to evaporate slowly until the balsam is of the required 

 density. 



On account of the small size of the eggs it was necessary to 

 cut very thin sections. For this purpose the hardest paraffine 

 ■was required ; the melting point ^of that used was fifty-eight 

 degrees centigrade (58° C). To get good sections the em- 

 bedding material must be perfectly clean, hard, and free from 

 bubbles ; these conditions can be obtained only by the utmost 

 care in manipulation and in the arrangement of details. Certain 

 advantages are gained by attention to the form of the blocks 

 of paraffine in which the objects are embedded ; they should be 

 in the shape of a triangle, the base, which is the shortest side, 

 being just wide enough to hold the object, and the altitude 

 about five or six times the length of the base. The apex of the 

 triangle is directed towards the edge of the knife, which, if 

 placed at an angle of 10° or 12° to the direction in which it 

 slides, will reach the apex of the triangle first, and cut a 

 closely rolled shaving of paraffine. The section of the object, 

 since it lies in the last portion of the section cut, will occupy 

 the outside roll ; it is obvious that, if the triangle was long 

 enough, the roll of paraffine would be so large that a section of 

 the egg would not cover more than one half the circumference. 

 The whole roll may now be placed on the slide, with the section 

 of the object down. When the slide is warmed, the melted 

 paraffine spreads the sections, and thus the trouble of unrolling 

 is avoided. 



If in cutting the sections the edge of the knife is placed at 

 right angles to the direction of motion, the sections will not 

 roll, but at the same time they cannot be cut so thin. 



