228 THE ROYAL SOCIETY OF CANADA 



for histological work. The fixing agent was a solution of ammonium 

 molybdate made up according to the following formula. 



Ammonium molybdate 1 gm. 



Distilled water 10 " 



Hydrogen peroxide -5 



A drop of hydrochloric acid is added to the solution and a pre- 

 cipate of molybdic acid forms, but readily redissolves on agitation. 

 To prevent maceration, a few drops of a 1% osmic acid solution were 

 added to the above mixture, and also to the water in which the dis- 

 section was carried out. The tissues of the stained caterpillar were 

 bathed in physiological salt solution, and the freshly made fixing 

 solution, cooled to near zero, was then poured on and left for several 

 hours. Material thus fixed remained in water indefinitely without 

 losing its colour. 



Preserved Specimens. During the winter months preserved 

 specimens were used after the fresh material was exhausted. Chloral 

 hydrate was used as the preservative and it proved an excellent 

 medium for preserving the internal organs. The finest nerves were 

 found to be in good condition after months of preservation. The 

 entire lateral sympathetic system was traced in preserved material. 



The dissection of preserved material is somewhat less difficult 

 than that of fresh material as in the former the muscles and fat body 

 have shrunken considerably. 



While it has been held by most workers that nervous tissue will 

 not take the methylen blue stain unless living or freshly killed, I have 

 succeeded in obtaining fairly satisfactory stains with preserved 

 material. The stain is of course much more difficult to obtain than 

 with fresh material and, when obtained, is not as good. Material 

 thus stained was not sectioned, and it is doubtful whether good 

 results would be obtained in histological work, but stained for dis- 

 section the nerves were well differentiated from the other tissues. 

 Some of the most difficult nerves were traced in preserved specimens 

 after first staining with methylen blue and fixing with ammonium 

 molybdate. 



The Central Nervous System. 



1. The Cephalic Ganglia and Nerves. 



The Supra-Oesophageal Ganglion. (Figs. 1 and 5, B.B.). 

 The brain consists of two large ovoid masses which show no differen- 

 tiation into neuromeres. This ganglion is situated in the dorsal 



