I20 



PSYCHE [June 



until the infiltrating is complete. This infiltration with pure paraftine will require 

 from three to twelve hours, depending upon the size of specimens, and character 

 of body wall. If it is necessary to interrupt the infiltration, the specimens in the 

 melted parafiine should not be allowed to cool slowly but the parafiine should be 

 hardened quickly by placing the paraffine dish on the surface of cold water and 

 plunging it beneath the surface as soon as a firm film forms over the top of the 

 paraffine. The paraffine can later be gradually melted and the infiltration pro- 

 ceeded with. When ready to imbed, pour some melted paraffine into a small paper 

 boat or into a watch glass and transfer the specimens into this boat or watch glass, 

 orienting them with a warm needle. Cool the paraffine quickly by putting boat 

 or watch glass into cold water. (Do not plunge beneath surface of water until film 

 forms on top of paraffine.) After cooling the parafiine, remove paper from around 

 the block, or cut the block out from the watch glass, and wrap up in paper or put 

 in a vial properly labeled. The specimens in these blocks may be kept indefinitely. 



Cutting. — The work of cutting sections with a microtome must be learned by 

 observation and experience. The many kinds of microtomes make any general 

 description of the process impossible. For cutting insect tissues, where the whole 

 body is sectioned or where any part of the body wall has to be cut, a heavy and 

 rigid microtome is necessary. The light, swift, wheel microtomes are not the best 

 for such work. I have found the large, heavy machine known as Minot's New 

 Automatic Microtome, with large knife rigidly fastened at both ends, the best 

 instrument, of several tried, for work with insects. The fixed knife and sliding 

 object-carrier automatically raised make possible the ribboning of sections, while 

 the horizontal position of the knife and the arrangement for the adjustment by hand 

 of the block for each cut make it possible to pay that special attention to each sec- 

 tion necessary in particular cases. With this microtome I have made complete 

 series of such heavily chitinized specimens as the pupae of blepharocerid flies or 

 the heads of various adult insects. With hard parafiine and a rigid powerful micro- 

 tome strongly chitinized insect cuticle can be successfully cut without distorting or 

 tearing the soft tissues lying next to it. For the study of the histolytic and histo- 

 genetic phenomena in the pupae of insects with complete metamorphosis it is neces- 

 sary to make uninterrupted series of complete body sections including the heavy 

 pupal cuticle. Hence the necessity of having in the entomological laboratory a 

 microtome capable of such strenuous work. 



The sections as cut may be transferred by brush or forceps or needle to a 

 sheet of paper until the cutting is finished, or may be put directly on the slide. 

 The slide should be well cleaned and dried and then smeared over with (almost) 

 the thinest possible coating of Mayer's albumen fixative. Arrange the sections 

 in regular order in lines transverse or longitudinal to the slide, and wiien it is 



