732 I^»- «J- BEARD, 



the true odontoblast pulp, though he did not recognise its nature. 

 The true pulp is, however, not so soft as appears from his description. 

 I have found it — especially in Bdellostoma — very hard indeed. 



I will now describe the appearances presented by a vertical section 

 of the median tooth of Bdellostoma^ and then compare it briefly with 

 the lingual teeth of the same animal, and afterwards with all the 

 teeth of Myxine. 



Such a section is partially figured in fig. 1, and in fig. 7. I have 

 given a semi - diagrammatic representation of the whole tooth. 

 Except in the diagrammatic arrangement of the pulp elements it is 

 fairly true to nature. Such a section is not to be made by means of 

 a razor; for it is impossible to soften the horn, and when the whole 

 tooth is embedded in paraffin it is as hard as a stone. 



Method. I have embedded such whole teeth in paraffin, and 

 afterwards, by means of a very strong knife a series of sections of 

 about one millimetre in thickness were cut ; only one or two of these 

 are of use. Those which pass near the centre of the tooth are then 

 fastened on a glass slide by means of canada balsam, and, after the 

 latter is hardened (in the warm oven), the section is ground down in 

 the manner practised by v. Koch for corals. To save time and to 

 obtain thinner sections with less trouble, one may file away a portion 

 of the thick section with a fine file before grinding it. 



Bdellostoma, 



The tooth of Bdellostoma is roughly divisible into three portions. 

 Outside of all is a c a p f h r n (fig. 7 h g), beneath this a strati- 

 fied epithelium (fig. 7 se) is met with, and finally more internal- 

 ly is situated the odontoblast pulp (figs. 1 and 7 oc). In Bdello- 

 stoma the outer horny layer is very thick and strong, and of a 

 bright yellow colour (fig. 1 Ji). Its diameter is about 0,275 milli- 

 metre and its length about 4 millimetres. 



It has the form of a cone over the pulp of the tooth, and is fitted 

 into an epidermal or horn groove (hg) at its base. It increases 

 in length from the cells of the horn groove becoming converted into 

 horn, and in thickness from the cells of the stratified epithelium. 



We may now pass to the description of the odontoblast pulp, 

 because certain other structures lying outside it are more easily de- 

 scribed after it. 



The odontoblast pulp is a hard, conical, massive, cellular 

 structure, which is very broad at its base (figs. 1 and 1 oc) and 



