882 W. H. GASKKLL. 



Those which I brought with me to Cambridge in 1888 were 

 kept alive iu a small basin containing sand and weed from 

 their native stream, the water in which was renewed occa- 

 sionally. They lived iu this way perfectly well, and some of 

 them are still living ; as far as I can see they have not grown 

 at all, or made the slightest attempt at transformation. The 

 others, which 1 have obtained lately, are kept in a large tank 

 with sand and weed in it. 



The method of observation which I have mainly relied on is 

 that of serial sections^ the whole head of the animal having 

 been embedded in paraffin, or else the brain dissected out and 

 then embedded. For hardening and staining I have used 

 various methods ; the whole head has been placed either in 

 osmic acid 1 per cent, solution, or else in Perenyi's fluid and 

 then alcohol, with subsequent staining in boro-picro-carmine 

 or picro-carmine and eosin : I have also stained on the slide 

 with aniline colours and with hsematoxylin. 



As a rule the sections are cut through the whole head and 

 mounted in order. By this means it is certain that all the 

 structures within the cranial cavity will be fixed on the slide 

 in their right position; but, on the other hand, there are in 

 many specimens hard parts in the region of the basilar plate 

 which turn the edge of the razor and tear through the neigh- 

 bouring soft tissues ; also so large a section is apt to be 

 crumpled when cut into ribbons by the Rocking microtome. 

 I have succeeded in getting over the folding of the sections by 

 a method which I have now used for some years past, but have 

 never as yet published ; it consists simply in floating the series 

 of sections on the surface of warm water and then transferring 

 them to the slide, which has been previously coated over with 

 albumen and glycerine. By this means the sections are 

 flattened ; they are then dried by pressure between blotting- 

 paper, the wax is melted, removed by xylol, and the series of 

 sections mounted in Canada balsam. 



The figures in Pis. XXV, XXVI, XXVII, XXVIII, are, for 

 the most part, drawn by myself, and by Mr. Wilson, of the 

 Scientific Instrument Company. I am indebted to Mr. 



