412 Mr. J. Blackwall's N(jtes on the Bahnon. 



this species in size wlieu restricted to fresh water, and from some 

 circumstances attending the loss of its teeth from the vomer. 



Adult salmon of average dimensions are known to have one or 

 two teeth only at the anterior extremity of the vomer, though 

 smolts have the same part amply provided with teeth extending 

 along a great portion of its length. In the summer of 1840 I 

 examined numerous specimens of salmon in various stages of 

 growth, for the purpose of ascertaining the period at which the 

 teeth begin to disappear from the vomer and the order in which 

 they are shed. Specimens weighing fx-om two to five pounds, 

 taken in the months of June and July, had from three to seven 

 teeth on the anterior part of the vomer, the number, allo^^ang for 

 the chfFerencc in condition, being almost always inversely as the 

 weight ; and individuals of a larger size, captured at the same time, 

 usually retained one or two teeth only, situated quite at its ante- 

 rior extremity. Other specimens weighing from half a pound to 

 a pound, taken in the month of August, were found to have the 

 vomer well supplied with teeth except at its posterior part, from 

 which some had been lost invarialjly. The situation which the 

 lost teeth have occupied is distinctly marked by dark spots in 

 small grilse, but as they increase in size these spots become more 

 obscure and, ultimately, are obliterated. 



As the teeth disappear from the vomer gradually and nearly in 

 regular succession, those at the posterior part being shed first, it 

 follows that the youngest fish, generally speaking, will have lost 

 the fewest ; consequently, the small grilse which ascend the Con- 

 way in August may be safely regarded as identical with the smolts 

 which descended the same river in the preceding spring. 



Having attempted to show that the growth of the salmon du- 

 ring its first visit to the sea is not so rapid as has been supposed, 

 I may state that I see no reason for believing that it is accelerated 

 in an extraordinary degree at any subsequent ])eriod of its life. 

 The salmon which come up the Conway annually exhibit every 

 gradation in weight from half a pound, or under, to twenty-five 

 and thirty pounds ; this would hardly be the case were the belief 

 in their extremely rapid growth well-founded, neither would in- 

 dividuals of large dimensions bear so very small a numerical pro- 

 portion as they are known to do to those of a medium size. 



In pursuing researches of this description it is desirable that 

 measurement should be attended to as well as weight, for salmon 

 of the same weight precisely often differ remarkably in their di- 

 mensions according to the condition they are in ; and the neglect 

 of this circumstance, I am inclined to think, has contributed 

 greatly to encumber the question with difficulties. 



I feel unwilling to offer any comments upon Mr. Young's ex- 



w 



