BRAINS OF THREE GENERA OF ANTS 517 



depends upon the caste, and after a little practice one can 

 sort the different castes before opening the cocoons. If the col- 

 lected material was too young to use it was found possible to 

 keep the larvae in artificial nests with a number of workers. 

 In every case the young were moved about and cared for by 

 the workers and developed in good condition. 



The fixatives used were Gilson's fluid, very good for both ner- 

 vous and other tissues and especially good for the fiber bundles 

 of the brain; Flemming's fluid, good for nerve cells though not 

 so good for nerve fibers; 10 per cent formalin, very poor, tending 

 to soften and disintegrate the tissues; Kalil's fluid, very good. 

 Cajal's method, used by Jonescu ('09) for the honey bee (namely, 

 silver nitrate in the dark at 30°C., followed by pyrogallic acid), 

 , was tried but without success. 



The material for sectioning was embedded in paraffin from 

 three to six hours, the sections were cut 6 ix thick and stained 

 on the slide. The most successful stain was Ehrlich's acid hema- 

 toxylin, followed by ammonia alcohol, and counterstained either 

 with eosin or Orange G. Iron hematoxylin is especially good 

 for differentiating the fiber bundles of the mushroom bodies. 

 Whole mounts of the heads were made by staining in Conklin's 

 picro-hematoxylin for a long time, twelve to forty-eight hours, the 

 longer time in the case of large heads like the Camponotus queens 

 and soldiers, and then destaining in 70 per cent acid alcohol from 

 six to twenty-four hours. After being dehydrated and cleared in 

 cedar oil the heads were mounted in damar, frontal side up. 

 When successfully destained all parts of the brain, the nerves, 

 the ocelli, and some of the glands of the head may be clearly 

 seen. The one disadvantage of this method is that it is not 

 permanent, the preparations fading after a few months, espe- 

 cially those that have had the prolonged treatment in acid alcohol. 



Borax carmine has also been used for whole mounts of the 

 heads, but although the preparations are permanent, they are 

 less transparent and show less than the hematoxylin mounts. 



