310 ENTOMOLOGY. 



once. Drain off the oil of cloves and put on a small quantity of 

 Canada balsam, or preferably balsam and benzole. Arrange the 

 creature on the centre of the slide. Let the balsam harden a little, 

 then the object will not float off, as happens sometimes when a 

 quantity of balsam is used at once. Lower the cover straight down 

 on the object ; do not try to drive out a wave of balsam as is recom- 

 mended in the text-books. It is better not to put enough balsam at 

 first to fill the space under the cover, as the balsam supports the 

 cover if it does not reach the edge; but if the balsam reaches the 

 edge of the cover it is apt to draw down the cover and crush delicate 

 objects. A few pieces of thin glass to support the cover are a great 

 protection to the object, or better still, a few tiny glass beads. 

 Finish the slide with a ring, Bell's cement or something of the kind, 

 but that must not be done unless the cover be supported in some 

 way. (Journ. Quek. Micr. Club, i. (1883), pp. 241-2.) 



Sections of the Brain. — In studying the brain of insects it is better 

 to begin with that of some of the lower forms, such as the cockroach 

 or locust, as they are on a simpler plan than that of ants, wasps, and 

 bees. In the sections of the brain, made by Mr. N. N. Mason in 

 1879, it was thought better to cut the entire head so that the muscles 

 and integument should support the soft parts within, including the 

 brain. The head therefore was cut with the microtome into sections 

 from -gjj-Q to yjjVo mcn m thickness, after having previously been 

 hardened in absolute alcohol for two days or more, and then kept in 

 melted paraffine for one or two or more days. It was then embedded 

 in a preparation of paraffine, sweet oil and wax, or, in some cases, in 

 soap. After the sections were cut they were stained with picro- 

 carmine, or with osmic acid and picrocarmine. Finally, the slices 

 were mounted in glycerine jelly for study under the microscope. 

 The sections were in most cases frontal ones, namely, cut transversely 

 from the front of the head or brain backwards, while a few were 

 longitudinal (vertical or sagittal) ones, viz., cut parallel to the median 

 line of the body. 



M. H. Viallaues, in his work on the brain of the locust (CEdipoda 

 and Caloptenus), published in 1887, describes his method as follows: 

 He separates the head from the living animal, then with the scissors 

 removes the labium and mouth-parts and all of the integument be- 

 hind the compound eyes. lie then removes the muscles of the man- 

 dibles, the tracheae and fatty masses, in order to expose the posterior 

 aspect of the brain. 



He then plunges the head thus prepared in a vessel containing the 

 following solution: Distilled water, 100; osmic acid, 0.02; acetic 

 acid, 0.50. At the end of a few minutes the brain is of a consistence 

 sufficient to allow the dissection to be finished without fear of 



