6 



but the majority of writers were inclined to credit thrips witli a 

 part, if not all, of this damage. As they had no means of iden- 

 tifying the little pest, they have usually referred to it as the 

 " grass thrips." This name has been very generally used for this 

 species, but not for any other so far as I can learn, and I have 

 therefore adopted it as the common name. 



Mkthods of Study. 



It was evident at the beginning of these studies upon the grass 

 thrips that the insects must be brought into the laboratory, where 

 close observations could be made upon individuals through all 

 their stages. For this purpose, large-mouthed, two-ounce bottles 

 were used. In these bottles specimens of the larvae taken from 

 the stems of " silver-topped June grass " were confined upon the 

 leaves of their usual food plant. The successive stages were ob- 

 served, and specimens mounted for more critical examination under 

 a compound microscope. In this way generation after generation 

 was followed through the year. It was found that mounts in 

 Canada balsam best preserved the coloration and natural appear- 

 ance of the insect. The most satisfactory results were obtained 

 by killing and allowing the specimens to stand for a few hours in 

 xylol before mounting in balsam dissolved in xylol. This method, 

 however, does not show the finer details of the external anatomy. 

 For these, the most satisfactory results were obtained by first 

 allowing the specimen to macerate in a ten per cent, solution of 

 potash from twenty-four to thirty-six hours, and then mounting in 

 glycerine. If the natural form of the body is desired, the speci- 

 men may be removed from the potash solution and boiled slightly 

 in a drop of glycerine upon a slide. This removes the potash 

 from the interior of the body, and renders it clear. The specimen 

 is then transferred to a cell, with glycerine as the medium. 



White zinc cement makes a very satisfactory cell, as it can be 

 built up rapidly, dries quickly, and, if properly finished, is very 

 firm and durable. In mounts made in this way over three years 

 ago the glycerine has had no appreciable effect upon the cement. 

 Zinc cells, however, require a few days to dry before becoming 

 firm enough for use. 



Better mounts for use with high-power objectives may be made 

 without a cell. The specimen may be transferred directly from 

 the potash to a small drop of glycerine upon the centre of a slide, 

 and covered with a slip. All surplus glycerine should be carefully 

 boiled out and removed with a small piece of filter paper. This 

 mount should also be finished with a coat of white zinc cement. 



