252 DR DAVY ON THE SALMONID^l. 



places of the cliarr. In this instance the young fish, after the disappearance of 

 the yolk, throve well, and, as I believe, chiefly on the infusoria present. This in- 

 ference was made partly in consequence of finding, on microscopic examination, in- 

 fusoria on the plants and stones and sides of the vessel, and vestiges of them in the 

 excrements of the young fish, and in the intestine of some that were opened, and 

 partly from observing how the young fish, when in pursuit, as it was supposed, 

 of food, seemed to confine themselves to the spots where the infusoria were in 

 greatest numbers. Another reason (were we to reason a priori on the subject) 

 might be assigned, viz., the presumed fitness of these microscopic animalcules for 

 the food of creatures of so small a size as the young of the Salmonidse in their 

 early stage, and the fitness of the latter, with their microscopic eyes, to see and 

 make the infusoria their prey. 



The fish, the subjects of these trials, were all young charr. Those from the 

 eggs impregnated on the 25th of November were so advanced by the second week 

 in April, as to be considered fit to be set at liberty. Some were taken to a lake 

 in the Highlands of Perthshire ; others to a mountain tarn in this neighbourhood. 

 Both sets were from the earthenware pan, to which no food had been given. 



I may offer as a suggestion, that where minnows abound, their young, it is 

 probable, may be employed as a useful aid for the support of the young of the Sal- 

 monidse. The time of breeding observed by the minnow, early in May, seems 

 suitable, and especially so the minuteness of the ova of this little fish, and of their 

 fry when hatched. Their eggs at maturity I have found to be 06 of an inch in dia- 

 meter ; the fcetal fish on quitting the egg was about "20 of an inch in length, and 

 no more than -35 inch when of its perfect form, as denoted by the growth of its 

 permanent fins, which it acquired in a few days. In this stage its weight (moist) 

 did not exceed -03 grain, and when dried was reduced to -01 grain ! * 



7. Of the Parr. 



As discussion, wherever doubt exists, is always useful, so that it be tempe- 

 rately conducted, and lead to further inquiry, I venture to bring under the notice 

 of the Society the question, the vexed question, whether there be or not a fish of 

 the family of the Salmonidse, a parr having so close a resemblance to the salmon 

 fry as to be with difficulty distinguished, and yet a distinct species. 



* 



The above results were obtained in the month specified. The eggs were from minnows from 

 the river Rothay, a tributary of Windermere. On the 6th of May, they were impregnated by the 

 artificial process, and placed in water, varying in temperature from 50° to 54°, which was changed 

 daily. One fcetal fish burst its shell on the 11th of May ; the next on the night of the 12th; the 

 majority on the following da) ; some did not appear till the 15th. On the 31st of the same month, 

 most of them had acquired their permanent fins. 



In substance, the eggs of the minnow were found similar to those of the Salmonidae, being com- 

 posed of oil globules, and of an albuminous fluid, coagulable by admixture with water. 



Some of the ova to which no milt was added — the omission intentional — died without showing 

 the slightest appearance of organic development. 



