1 66 PEABODY. [VOL. I. 



and mounted in a mixture of dilute glycerine and ammonium 

 picrate. If the slide is sealed with asphaltum the preparation 

 may be kept for several weeks. The sections are best studied 

 at once, however, as the blue tends either to fade or to become 

 granular, the fibrillae losing their continuous appearance. 



My experience with methylene blue as applied to selachian 

 material has led me to the following conclusions: (i) The 

 tissue must be alive when the blue is applied. I have never 

 had a successful impregnation unless the head is removed from 

 a live animal and injected at once. (2) The strength of solu- 

 tion seems unimportant, since I have obtained a good stain 

 with such extremes as li^o and J^. (3) The most impor- 

 tant facts to be learned to obtain success with a given tissue 

 are, first, the time which the stain should act on the tissue 

 before exposure to the air, and second, how long an exposure 

 is necessary. The time limits which give success with dogfish 

 do not give good results with skates. (4) The best results are 

 obtained from ampullae which seem scarcely tinged with the 

 blue. When the tissue is deeply stained one finds on exami- 

 nation with the low power of the microscope that the stain is 

 located in the cells, not in the fibers. (5) It is impossible to 

 carry the methylene blue through the paraffin bath unless the 

 tissue is completely dehydrated, hence the importance of secur- 

 ing genuine absolute alcohol. (6) I have been unable to pre- 

 serve the stain in alcohol or in the clearing oils for any length 

 of time. I have cut paraffin blocks, however, a year after the 

 objects were imbedded, and the blue seems perfectly preserved. 

 This seems the surest means of preservation of the stained 

 tissue till one is ready to use it. Sections mounted in balsam 

 or dammar in August, 1895, have not lost a bit of their 

 clearness. 



Groups of Ampullae. - - Following Ewart's nomenclature I 

 shall designate the groups of ampullae according to their inner- 

 vation as supra-orbital, buccal, hyoid, and mandibular. In 

 Galeus it seems impossible to distinguish the supra-orbital and 

 buccal. 



In order to determine the number in each group the am- 

 pullae were carefully dissected out and counted in two speci- 



