460 CHAELES S. TOMES. 



functions goes, so long as it is sufficiently strong, sufficiently 

 sharp, and of an appropriate shape. Hence it appeared to be a 

 matter of interest to ascertain what the extent of this variation 

 in structure is, and to see how far these differences are found 

 to coincide with the lines of classification which have been 

 adopted on general grounds. 



As a preliminary to this inquiry I sought to ascertain how 

 far the Gadidse are to be regarded as a good natural family ; and 

 being perfectly unable to myself form any opinion upon this 

 point, I consulted Dr. Giinther and Mr. Boulenger, who will 

 be acknowledged to be in a position to speak with the highest 

 authority. 



They tell me that the Gadidse are a well-marked and natural 

 group, and therefore well adapted for the purpose of such an in- 

 vestigation ; to their kindness I am indebted for the opportunity 

 of examining several genera not otherwise accessible to me. 



The teeth of the Gadidse all consist of that modification of 

 dentine which is known as vasodentine proper, and, as there is 

 still a little confusion in the application of this term by various 

 authors, it seems desirable to very briefly define what the 

 meaning of the term really is ; this I did some years ago at 

 greater length (1). 



Retzius (3) was the first to describe the tissue accurately, 

 but he did not give to it a distinctive name. Owen (2), fol- 

 lowing in his footsteps, gave it the name of vasodentine^ but 

 at the same time included certain other forms of dentine which 

 hardly come under the same category. 



In 1878 (1) I endeavoured to carry further the existing 

 descriptions, and to point out that the term vasodentine should 

 be limited to those dentines in which, in the words of Retzius, 

 the larger canals " formed, with others of the contiguous tubes, 

 large loop-shaped anastomoses, and the outer extremities 

 entered also into closed anastomoses, almost like the more 

 minute blood-vessels in the villi of the abdominal canal." 



I also pointed out that in the fresh state these canals 

 contained capillary blood-vessels through which red blood 

 circulated, so that a typical vasodentine tooth in the living 



