40 SALMONID^ OF BRITAIN. 



that stortly after extrusion from the parent some eggs at once largely increase 

 in size by the direct imbibition of water, but this does not prove that there is a 

 constant current through the shell, while the following experiments distinctly 

 show that such could not invariably be the case. Eggs, it is well known, 

 are sent long distances, as to the Antipodes, in moss,* and, if necessary, kept 

 cool by means of ice ; in such cases sufficient dampness is present to enable 

 imbibition to occur through the egg-shell, but there is water whereby a current 

 could be kept ap, yet the embryo develops, thus clearly demonstrating that 

 moisture without immersion is sufficient for incubation, provided the eggs are 

 kept cold, dark, and damp. In such cases oxygen or gas alone could be absorbed, 

 while the presence of moss would assist in carrying off excreted carbonic acid. 

 Should the egg be placed on a piece of glass or other smooth substance, and 

 kept moist, it soon dies, the water which attaches it by its base to the glass 

 probably becomes charged with the excreted carbonic acid, which, reacting on the 

 embryo, is as a poison to it. 



In order to ascertain whether this absorption of oxygen occurs solely at the 

 micropyle, or throughout the general surface of the egg-shell,t the shells of two 

 trout eggs were emptied of their contents, and the portion where the micropylej 

 is situated was removed, and in each instance a solution of picrocarmine passed 

 through the shell showing its permeability. 



Salmonoid eggs may even be successfully incubated in water that is nV)t 

 flowing, thus — on December 15th, 1885, ten trout eggs were placed in a tumbler 

 wherein the water was changed daily ; one died, the remainder hatched between 

 March 25th and 28th. On February 4th, one egg was similarly treated, except 

 that the water was changed on alternate days — it hatched on March 26th. 

 On February 12th, six more trout eggs were placed in a tumber in which the 

 water was renewed every third day, and all hatched between March 27th and 

 April 6th. 



The influence of light upon the eggs of Salmonidse has a decidedly deleterious 

 effect ; while during incubation the embryo, as a rule, appears to lie with its 

 eyes uppermost. Should an excess of light be allowed, the contained young 

 eeems to be badly developed, and has small and dark eyes ; while any alevins that 

 are hatched are, as a rulej weakly. It may be for this reason that redds are 

 constructed, in order to keep the eggs in the dark, or it may be also for the 

 purpose of preventing movement in their earlier stages. 



The dangers of transporting salmonoid eggs, except at certain periods and 

 under exceptional conditions, have already been alluded to (pp. .31, 32 ante), and 

 here the effects of injuries or shocks which ova can sustain and yet survive have 

 to be considered. Slight shocks may be reasonably anticipated to frequently 



* Feb. 27tli, 1886, I was shown at Howietoun some hundreds of eggs of the Loohleven trout, 

 and a few of the salmon, the former of which had been taken from the fish on December 19th, 

 when they were placed in a hatching- tray. On January 22nd they were removed to damp moss, 

 on which a little ice was laid, and had been subsequently kept in a room in which the tempera- 

 ture only varied between 40° and 44° Fahr. I took the box of eggs as they were to Cheltenham, 

 and on March 2nd placed a few in a hatching-tray, leaving the remainder in the moss. Those in 

 the trays commenced hatching on March 26th, on the 106th day, when ten came out ; and two 

 days subsequently, on looking at the eggs which had been left in the moss, in which the tempera- 

 ture stood at 55° Fahr., one was found hatched, twelve dead, so the rest of the ova were placed in 

 a hatching-tray, and came out in due course, whether of salmon or trout. Some of the foregoing 

 eggs were removed from the damp moss on March 9th, and placed in tumblers of water in a 

 warm room, and commenced hatching on the 16th, or 96th day. (For a detailed account see 

 The Field, May 8th, 1886.) 



+ Eespecting whether the air in solution in the water is or is not conveyed directly to within 

 the ' ovum conflicting opinions have been held. Dr. John Davy {Physiologieal Besearches) 

 questioned if the shell of the egg among the Salmonidse, when in a sound state, before putrefac- 

 tion had commenced, could be pervious to water, as asserted by Vogt ; but both agreed that the 

 death of the impregnated ovum or embryo is clearly demonstrated by the coagulation of the yelk 

 from penetration into its substance. 



} To see whether, after death, water obtains access to the interior of the egg through the 

 micropyle, the experiment was tried of placing ova in water just suiEcient to cover them 

 two-thirds up their sides, leaving the micropyle dry, but the changes were similar to those in 

 other eggs in which the micropyle was submerged. 



