EGGS INCUBATED EST MOSS— TEMPERATURE. 35 



they have eyed, they may be left for twelve or more hours in damp moss, when the 

 weak ones will often be distinguishable by their pale appearance. 



When the eggs commence to hatch considerable attention is necessary, while 

 somewhat different treatment may be required in accordance with the method 

 which has been adopted. In the glass grille system the young slips through 

 between the rods on to the bottom of the box, but as it then comes in contact 

 with the discarded egg-shells, which are decidedly injurious, one plan is to turn 

 all the eggs ofE the grilles on to the box and slightly raise the depth of the water. 

 Or, if perforated zinc trays are employed, the use of the watering-pot may be 

 necessary in order to remove the discarded egg-shells and other impurities. Some 

 fish are seen to hatch by the egg splitting down the line of the back, others 

 emerge tail first or head first, this last being frequently effected at the great 

 danger of a portion of the sac becoming forced before the head at the risk of 

 suffocating the alevin. Some on emerging are lively and strong, while others on 

 the contrary are listless and weak ; occasionally a little assistance is necessary in 

 order to help the little fish out of the shell, and for this purpose some fish-calturists 

 recommend the use of a camel-hair brush. If the trays are sufficiently large, 

 the young salmon and trout may be kept two or three months in the hatching- 

 house, and char still longer. 



Although experiments have shown that eggs may be successfully incubated in 

 damp moss, it would seem that a sluggish current of water may be equivalent to 

 a diminished supply of proper aeration, and merely sufficient for the slow develop- 

 ment of the embryo. On December 12th, 1885, a number of trout eggs, which 

 had been obtained from the fish the previous day, were received in a swing tin 

 can at Cheltenham, from Howietoun : they were placed inside a coach-house in 

 hatching-trays supplied with a slow stream of water from a tub, filled twice or 

 more daily from a contiguous well. As the water was only sufficient to pass in 

 the form of a small stream from thirty to forty times a day through' each 

 incubating tray, it is clear that they miist have received merely a minimum of 

 aeration. On December 21st, Mr. Ogden had about 200 of these eggs, which he 

 took to Matlock and put in hatching-trays in a good stream of water, where they 

 hatched upwards of a month before those which were kept at Cheltenham.* 

 Consequently deferred hatching, or protracted incubation, may not invariably be 

 a good sign or the certain forerunner of strength in the young.f 



It has been shown that the temperature of the water employed exercises a 

 considerable influence upon the time required for incubation, and Seth Green 



* Another subject of interest was the date at which the trout eggs hatched during the season 

 of 1885-86, at Cheltenham, for in 1884-85 they eommenced on the 82nd day, but not in large 

 numbers until the 87th day, while in the winter of 1885-86 the first emerged on the 103rd day, and 

 the main body began to show themselves on the 106th day. As during these two seasons the 

 eggs were incubated in the same house, with water obtained from the same pump and likewise 

 in nearly the identical apparatus, the conditions were almost similar. But doubtless a lower 

 temperature was one of the causes, and I have been furnished by my neighbour, Mr. Tyrer, with 

 the following comparative statements of the temperature of the two seasons under review : — 



Season 1884-85. Season 1885-86. 



. 38-0 



. 35-0 



. 33-6 



. 39-6 



Mean monthly temperature . . 39-9 .... 36-5 

 Although the mean temperature of the four months in the open air, in 1885-86, was 3-4S below 

 that of 1884-85, that of February, 1886, was nearly 10" below that of 1885. The figures show that 

 in the latter season the temperature was 3 J degrees colder than in the former one, or a difference 

 of about 174 days, computing by Seth Green's table, which was within IJ days of the actual 

 period. 



t In the course of my experiments carried on during the season of 1885-86, at Cheltenham, 

 it must not be taken for granted that everything invariably went on smoothly, for accidents 

 occasionally took place. Thus, one Sunday it was thought that instead of fresh water being 

 pumped in order to fill each reservoir tub, that which had passed over hatching eggs would do 

 just for that day only. This water, however, had the usual appearance seen at this period, 

 being covered with a sort of soap-suddy foam, and highly deleterious for this purpose ; it, however, 

 was tried, and with the result of a large number of deaths resulting. 



3 * 



