4 BULLETIN OF THE 



minutes, the slide, wliile warm, is thoroughly washed with flowing tur- 

 pentine. This can be applied conveniently from a small wash-bottle. All 

 of the paraffine should be removed from the slide before it becomes 

 cool, otherwise on cooling some paraffine may solidify. This is liable to 

 loosen the film of collodion. The wash of turpentine should be contin- 

 ued not only till the paraffine is thoroughly removed, but till the slide is 

 cool. Then, and not till then, can the turpentine be safely replaced by 

 alcohol, first 95%, then 70%, 50%, and 35%, and finally it can be im- 

 mersed in water. After once having got the slide with its sections into 

 water, the subsequent treatment with alcohol and water seems to have 

 no effect in loosening the sections, although the film of collodion will 

 dissolve easily in ether. I have veiy generally employed this method 

 of staining for two years, and as it obviates the dilliculties which arise 

 from maceration or partial penetration of dyes, I use it in jDrcference to 

 staining in toto. I have lost very few sections by it, and such accidents 

 as I have had were due, I believe, to a neglect of some of the precau- 

 tions which have been mentioned. 



The method of staining nerve-fibres which I have employed consists 

 of a modified use of Weigert's haematoxylin. The tissue which was 

 stained by this method was for the most part killed in hot water, 

 although I have also successfully stained nerve-fibres which were killed 

 in chromic acid and Kleinenberg's picro-sulphuric acid. Sections of the 

 optic nerve which had been mounted on the slide and carried into water 

 were treated for about half a minute with an aqueous solution of 

 potassic hydrate 1^0%. They were then thoroughly rinsed in distilled 

 water and transferred to Weigert's hsematoxylin. Here they remained 

 for about three hours at a temperature of 50° C. They were then 

 rinsed again in distilled water, carried through the grades of alcohol, 

 and after being dehydrated with alcohol of about 99%, they were cleared 

 in turpentine and mounted in benzole balsam. Each nerve-fibre when 

 so treated had a distinct blue-gray outline. The sections do not over- 

 stain even when they are kept in the dye for a prolonged period, and 

 there is of course no subsequent decoloring. This method yields fair 

 results when applied to nerves from any part of the lobster's body, but 

 it is especially successful in treating that portion of the optic nerve 

 which intervenes between the retina and the optic ganglion. 



The Histology. 



The two movable eye-stalks of the lobster are situated one on either 

 side of the rostrum, at the angle which that structure makes with the 



