210 Journal of Comparative Neurology. 



and it is surprising to find on what few types our knowledge 

 rests, the frog, rabbit and human subject being the regular 

 stand-bys. As nothing to my knowledge had been done on se- 

 lachians I thought it might be worth while studying the condi- 

 tions there presented. My results soon gave me reason to 

 believe that this hope had not been misplaced and that the ter- 

 mination of the sensory nerves in the selachian cornea was 

 evidently different from that of amphibians and mammals ac- 

 cording to the classical researches of Hoyer, Arnold, Izquierdo, 

 Klein, Kolliker, Dogiel, and so well worthy of further study. 

 The following remarks apply to some short and very imperfect 

 work which I have done on the subject within the last few 

 months. The material I have used mostly was from the ordi- 

 nary form of " Smooth dog fish " (Mustelus canis) so abundant 

 here, although I have secured the corneas from the following 

 sharks occasionally : Galeocerdo tigrinus, Carcharhinus obscurus, 

 Sphyrna zygaena, Carcharias littoralis, for all of which the fol- 

 lowing results also hold. 



The methylen blue method of staining was adopted and 

 so far I have used it only. The particular modification of the 

 blue method used was that recommended by Dogiel (3). 

 Apathy's (4) fixation also gave good results, but for thorough 

 action Dogiel's fixation is more to be depended upon. Bethe 

 fixation (5) has been used for sections, but on account of the 

 trouble experienced in cutting I have had few results with it, 

 for the cornea tissue proper so hardens in the usual processes 

 of embedding that it is nearly impossible to cut it. At first I 

 had trouble with my fixing fluids in that they caused too much 

 maceration. This was stopped by adding a few drops of i-io 

 per cent, solution osmic acid, which was not enough to blacken 

 the tissues, and so render them obscure. 



A few words as to the general histological structure of the 

 cornea in Selachians. 



The anterior corneal epithelium is somewhat thicker al- 

 together than that of the cornea stroma proper, composed of 

 large cells, having centrally placed rounded nuclei. The epi- 

 thelium is on an average 12 to 18 layers of cells deep, the su- 



