ADDITIONAL NOTES. 301 



provided in its yolk-bag, may for some days, as requiring 

 no food ab externo, be easily conveyed from place to place 

 in confined portions of fresh water. Judging from the analogy 

 of the young salmon, and from what I have learned respect- 

 ing the young trout, its time of easy and safe conveyance 

 may be extended to a few weeks, at least five and probably six 

 or seven. We are informed by Mr. Young, in his " History of 

 the Salmon," that the internal yolk-bag protruding from the 

 abdomen of the young fish, does not disappear till the end of 

 the fifth week, reckoning from the time of hatching; nor, I 

 believe, does it disappear earlier in the instance of the trout. 

 Moreover, as in the young of those cartilaginous fishes which 

 have been examined, the internal yolk-bag has been found to 

 increase as the external has diminished, reasoning from analogy, 

 it may be inferred that the same probably occurs in the instance of 

 the Salmonidae, and consequently that they have included within 

 themselves a store of food in the inner yolk-bag, sufficient to 

 support them altogether or in part, considerably beyond the fifth 

 week. In a young torpedo which I examined when six months 

 old, a vestige of the inner yolk was even then discoverable. There 

 are other circumstances which may be mentioned as favourable 

 to the transport of fishes shortly after hatching, viz. their greater 

 irritability and tenacity of life, denoted by the length of time 

 their heart continues to act when removed from the body, and 

 the season of the year, the winter season, when the colder 

 water has a larger proportion of atmospheric air, and retains 

 it longer than* the warmer water of a milder season. J. D. 



( On the Digestive Powers of the Salmonidce, page 112.) 



The author alludes to the digestion of the salmon as being 

 very quick. It appears to be so in all the Salmonidse, and is 

 probably connected with power of rapid growth, which is 

 so remarkable in the majority of them, when abundantly 

 supplied with food. Proof of such quickness of digestion 

 is often afforded in the dead fish ; often and often I have 

 found in the trout and salmon-fry that portion of its abdominal 

 parietes, corresponding to the lower part of the stomach, and 

 the upper part of the intestine, reduced to a soft, pulpy state, 

 approaching to chyme, and not ^infrequently a portion, also, of 



