128 



THE AMERICAN NATURALIST. [Vol. XXXVIII. 



caught were males. A number of females were found, but 

 never on the wing. They were always either in the grass, or on 

 some low plant where they could easily have climbed. 



Three methods of fixation were tried the first summer. For 

 two of these the insects were killed by dropping into hot water. 

 The caudal part of the abdomen was then clipped off and put 

 into the fixing fluid without removing any part of the chitin. 

 Half of this material was fixed for twenty-four hours in Flem- 

 ming's solution (strong). This proved almost worthless, with 

 the exception of a single slide. The other half of this material 

 was fixed in Gilson's mercuro-nitric solution for seven hours. 

 This gave very good preparations of the general features of both 

 layers of the light-organs. 



The third lot of material was killed and fixed in hot 70% 

 alcohol. This was satisfactory for the gross structure of the 

 organs, though not good for the finer details. 



The second summer the killing of the insects in hot water was 

 abandoned. The cadual portion of the abdomen was clipped off, 

 the tip cut away, and the dorsal wall removed to insure better 

 penetration of the fixing fluid. The living tissue was then put 

 directly into the fi.xer. Flemming's fluid, after this treatment, 

 gave mucli better results than before. Hermann's fluid gave a 

 tairly good fixation. The cells of the cylinders are definitely 

 ovitlincd in these preparations, but the tissues in general are 



By tar the best results for the tracheal stfuctures were 

 obtained by the use of osmic acid. The strength of the acid 

 was varied Ironi , 1 to \ and the time of fixation, from two 

 thirty hours. The l)est preparations were from material left 



Material fixed in I-"leinnnng's or Hermann's fluid, or in osmic 

 acid, was washed tor twenty-four hours in running water. That 

 fixed in (iilson's Huid was 'put directly into 70^' alcohol. All 

 the material was dehydratetl by carrying it through the grades 

 "t alcohol, from jo'/r to absolute. Cedar oil was used for 

 dealing. These sections were all cut in paraffin. 



The greater part of the sections were cut 10 in thickness, 

 )ut a few thinner sections. 3 and 5 /n, were made for the deter- 



