ORIGIN OF CASTES OF TERMITES 103 



I am indebted for specimens of the young of both L. virginicus 

 and L. fla^dpes. The photo-micrographs shown in figures 38 

 to 42 were taken, from sHdes made by the writer, by Mr. John 

 H. Paine, of the Bureau of Entomology, United States Depart- 

 ment of Agriculture, and I wish to thank the Bureau of Ento- 

 mology for the many courtesies extended to me. 



The nests were foimd in the interior of partly decayed logs, 

 which were chopped open, and the young nymphs were then 

 picked up with fine forceps and dropped at once into the fixative. 

 Bouin's fluid, which has proved most successful for the older 

 stages of Leucotermes, was the chief fixative used; and it is verj^ 

 satisfactory for all except the youngest nymphs. For these, a 

 fixative with a more rapid penetration would be better; Bouin's 

 fluid penetrates slowly, and if the digestive tract contains much 

 food, the posterior part of the intestine and sometimes even the 

 oesophagus is protruded, injuring the end of the abdomen and 

 the sex organs, or the brain. Unfortunately I did not discover 

 this until the collecting season was past, but out of the large 

 numbers of very young njrmphs collected there were many in 

 good condition. One lot of material fixed in alcoholic corrosive- 

 acetic gave excellent results. 



Before staining it is necessary to puncture the body cuticula 

 with very fine needles sharpened on a stone. For preliminary 

 study whole mounts were made of the entire insect by staining 

 for two days in Conklin's picro-haematoxylin and destaining 

 in acid alcohol from thirtj'-six to forty-eight hours, imtil the de- 

 sired differentiation was obtained. The specimens were then 

 rapidly dehydrated, otherwise they become very brittle, cleared 

 in cedar oil by the sinking method, and mounted in damar. 

 Meyer's carmalum was also tried for staining whole mounts, 

 but although it is more permanent than the picro-haematoxylin, 

 it gives a much less sharp differentiation and has not been used 

 to any extent. 



The specimens to be embedded and sectioned were also stained 

 by the Conklin method, and each individual was examined in 

 cedar oil under the dissecting lens in order to determine the type, 

 sex, etc.; the different types were then kept separate. The 



