314 ENTOMOLOGY. 



the excess llieu removed with acid alcohol in the usual manner. 

 The sections were then mounted in balsam. 



In order to demonstrate the presence of the corneal kypodermu in 

 the facetted Arthropod eye, and the connection of the so called 

 '• rbabdom" with the crystalline corie-eells, Mr. Patten ^ays it is neces- 

 sary to resort to maceration. In most cases it is hardly possible to 

 determine the important points by means of sections alone. 



The ommateum of fresh eyes, treated for twenty-four hours or more 

 with weak sulphuric or chromic acid, or in Mailer's fluid, may be 

 easily removed, leaving the corneal facets with tbe underlying hypo- 

 dermis uninjured. Surface views of the cornea prepared in tbis way 

 show the number and arrangement of the corneal cells on each facet. 

 In macerating the cells of tbe ommateum it is not possible to give any 

 definite directions, for the results vary greatly with different eyes, and 

 ic is also necessary to modify the treatment according to the special 

 point to be determined. It is as essential to isolate the individual cells 

 as it is to study cross and longitudinal sections of the pigmented eyes. 

 In determining the number and arrangement of the cells and the dis- 

 tribution of tbe pigment, the latter method is indispensable; it should 

 not be replaced by the study of depigmented sections, which should 

 be resorted to in special cases only. 



In fixing the tissues of the eye, it is not sufficient to place the de- 

 tached head in the hardening fluid: antennae and mouth-parts should 

 be cut off as close to the eye as possible, in order to allow free and 

 immediate access of the fluids to the eye. When it is possible to do so 

 with safety, the head should be cut open, and all unnecessary tis-ue 

 and hard parts removed. With abundant material, one often finds 

 individuals in which it is possible to Beparate, uninjured, the hardened 

 tissues of the eye from the cuticula. This is, of course, a great ad- 

 vantage in catting sections. The presence of a hard cuticula is often 

 a serious difficulty in sectioning the eyes of Arthropods. This dif- 

 ficulty can be diminished somewhat by the use of the hardest par- 

 afline, and by placing the broad surface of the cuticula at right angles 

 to the edge of the knife when sectioning. Ribbon-sections cannot be 

 made with very hard paraifine, but it is often neees-ary to sacrifice 

 this advantage in order to obtain very good sections. (Roy. Mic. 

 Journ., Aug. l vv 7. i 



Expanding and Mounting the Tongue of the House- and Blow-fly. — 

 C. M- Vorce remarks that if the head of a living fly be cut off, the 

 tongue will usually retract; pressure on the head will expand the 

 tongue, but unless it be secured by Borne means Ix-fore the pressure on 

 the head is released, it is apt to wholly or partly retract again. "If 

 only the tip is wanted, it i- easily secured by placing the severed head 

 on a clean slip and pressing with a needle till the tongue is fully 



