220 Annals Entomological Society of America [Vol. IV, 



present paper is a continuation of the study of the nervous 

 system in the larval form and, although not as complete as 

 might be wished, it is at least a start in the direction of a clearer 

 comprehension of the insect central nervous system, under- 

 taken for the purpose of preparing for a study of the finer 

 structure of the nerve cells, and for experiments upon their 

 metabolism and function. 



The methods employed were various. For obtaining the 

 best idea of the general distribution of nerve cells and fibers, and 

 the tracts of which they are parts, intra vitam methylene blue 

 injections were used. Beautiful results were obtained at 

 times, but it was only after hundreds of specimens were gone 

 over that much was learned as to the organization of the gan- 

 glia. Sectioning methods with the usual fixers and stains gave 

 fair results and the methods of Golgi and Cajal were tried, also 

 those of Villanes and Kenyon. All of these gave good prep- 

 arations except the Golgi method which I hope to try again at 

 another time. There were difficulties in the way of fixing and 

 staining because the ganglia are inclosed in chitin and because 

 of the numerous tracheal vessels, and in the larger out s it wa? 

 not possible to get perfect whole mounts. Sketches were 

 made from the methylene blue preparations both before and 

 after fixation and in the first stages of the work peripheral 

 nerves were traced by means of gross dissections. 



ABDOMINAL GANGLIA. 



The abdominal ganglia, eight in number are quite uniform 

 in appearance and general structure with the exception of the 

 eighth or most caudal. The first abdominal is separated by only 

 short connectives from the third thoracic, and the seventh is 

 even closer to the eighth. The seven first abdominal ganglia 

 have quite uniformly on each side, two large nerve trunks 

 connected with them, a cephalic lateral and a ventral more 

 caudal branch. The eighth ganglion has four pairs of branches 

 leading into it from the caudal end of the animal. 



Specimens were injected with methylene blue and nerves 

 traced to the periphery and from here followed into the ganglia 

 as nerve tracts as far as possible. In an earlier study on th^ 

 nervous system of larval insects I found that in some cases 

 some of the more cephalic branches connected with the ganglia 

 were in large part if not totally sensory, that is arising from 



