Humphrey, Brain of the Snapping Turtle. 75 



were hematoxylin and picric-acid-fuchsin. Experimentation 

 with these gave better results than any other stains tried. Of 

 the various hematoxylins, Delafield's formula gave the best re- 

 sults, though Gage's was usually satisfactory. The picric acid- 

 fuchsin stain combined with the hematoxylin is especially good 

 for work of this character, the hematoxylin staining the cells 

 the characteristic color, while the fuchsin stains the fibers a 

 cherry red and all connective tissues a very deep red. It was 

 found that the following mixture of these stains would give as 

 good results as to stain with them separately. 



Sat. Aqu. Sol. picric acid 20 cc. 



" " " Fuchsin 5 cc. 



Delafield's hematoxylin 75 cc. 



This mixture gives every indication of being permanent. Sec- 

 tions stained forty-five minutes with this mixture and allowed to 

 bleach slightly in thirty-five per cent, alcohol, gave good results. 

 A mixture with the hematoxylin increased to 100 cc. stains 

 more rapidly. All figures were outlined with the Abbe camera 

 lucida and details filled in with higher magnification. 



Ectal Features of the Brain. 



Cranial Cavity and Brain Membranes. — The cranial cavi- 

 ty of Clielydra is very large compared with the size of the brain, 

 the latter in the adult occuping not more than one third of the 

 space. This cavity is lined with a tough firm dura that slightly 

 adheres to the bony walls and is carried out as envelope around 

 the cranial nerves. The presence of this membrane renders the 

 tracing of the cranial nerves through the thick walls of the skull 

 comparatively easy, but makes the isolation of the separate 

 nerve roots and branches difficult. Entad of the dura is the 

 well developed arachnoid uniting the dura and pia by connect- 

 ing threads. These threads are few in the cephalic regions of 

 the brain but are especially numerous about the metencephal. 

 The pia, compared with that of other animals, is tough and 

 firm, adhering closely to the brain surface. Many minute blood 

 vessels pass through the pia and deeply penetrate the brain. The 

 close adhesion of the pia and the presence of these penetrating 



