64 Annals Entomological Society of America [Vol. X, 



MATERIALS AND METHODS. 



Although the histological investigation of this problem was 

 limited to two species, Ergates spicidatus Lee. and Monohanimus 

 confusor Kirby, larvae of other genera were examined to deter- 

 mine the presence and arrangement of the organs. Among 

 these larvae were specimens of Saperda Candida Fabr., Rhagium 

 lineatnm Oliv., Dcsmocenis palliatus Forst., and Mallodon 

 das y stomas Say. 



In dissecting out the structure for toto preparations, best 

 results were obtained by opening the larvas on the mid dorsal 

 line, and pinning them open in a watch crystal which had been 

 half filled with paraflEin. As a dissecting medium, picric alcohol 

 was very satisfactory. In addition, Delafield's haematoxylin 

 was frequently used to aid in dififerentiating the tissues for gross 

 dissection. For mounts of the entire organ, staining with 

 borax carmine was very satisfactory. Portions for sectioning 

 were obtained from the fresh larvae by cutting out the parts in 

 each segment which contained the organs, and placing these 

 directly into fixing fluids. 



The parts for histological study were fixed in strong Flem- 

 ming's solution for twenty-four hours, washed thoroughly, and 

 dehydrated by the usual process. However, formol-chromic 

 acid, as used by Schwabe, was found very satisfactory for fixing 

 these organs. The material was infiltered in 54° paraffin for 

 three hours, then in 58° paraffin for one hour, and imbedded. 

 Sections were cut two, three, four, and five microns thick. For 

 the study of cross sections, those cut two and three microns 

 thick were more satisfactory, but for longitudinal sections, 

 those cut at five microns were best, as it was very difficult to 

 obtain thinner sections that showed the internal structures. 

 For staining, Heidenhain's iron haematoxylin was found the most 

 satisfactory. 



LITERATURE. 



Before taking up the description of these structures, we shall 

 discuss briefly the more important work that has been done 

 upon the chordotonal organs in insects. It is very probable 

 that more has been written on these structures in the adult 

 Orthoptera than in all the other insects together. Although 

 many authors have described these organs in the insects of 

 other orders, very little attention has been given to their 

 condition in the larvae. 



