114 BULLETIN OF THE BUREAU OF FISHERIES. 



fibers. Yet the majority of the salmon taken at Cazadero show on the averagie as much 

 intracellular fat as is shown in those salmon taken from the Columbia River at a much 

 earlier stage in the migration. Certainly they show as much fat in the fibers as all but 

 the very fattest of the earlier specimens. It is this showing which presents such a strik- 

 ing factor in the comparison between the pink muscle of different salmon at the various 

 stages. The pink muscle maintains a surprisingly large amount of intracellular fat 

 throughout the whole series of stations, even when the fat is practically eliminated from 

 the great storage depots. 



In the case of the dark muscle, which at the early stages is surcharged with fat, 

 there is an obvious gradual diminution from the mouth of the river to the spawning 

 ground. On the other hand, there is no complete elimination of fat below that stage of 

 smallest liposomes which characterizes the pink muscle as a type. The fat n^y be 

 eroded from the dark muscle; that is to say, the large drops will gradually decrease in 

 size but will never be completely eliminated. There is some factor operating which 

 maintains a supply of liposomes in the active muscle of the major portion of the body. 

 It is true this supply is not kept up in the caudal muscle, but this undoubtedly is due 

 to the great and continuous activity of that musculature. 



Cheek muscle. — The amount of fat in the cheek muscle has been described for fish 

 from Ilwaco, but this particular type of muscle has not been studied in all the interme- 

 diate stations. However, in one specimen, no. 140 from Cazadero, this muscle has been 

 carefully reexamined. The fibers of the muscle of this fish are even more compact than 

 noted at Ilwaco. There is only a small amount of interstitial connective tissue and 

 this carries a few scattered but small fat droplets. 



The intracellular fat is present only in traces. In a large proportion of the fibers 

 no fat can be distinguished; yet in a few of the smallest fibers merest traces are dis- 

 cernible. 



The striking characteristic of the cheek muscle of no. 140 is found in the evidences 

 of degeneration. Certain of the fibers take a definite stain not due to the fat, but due 

 to characteristic degenerative changes in the fibers. These fibers stain a light rose 

 pink. Under the oil immersion the fibers that take this special stain show signs of 

 disintegration or atrophy. The bodies of the fibers have greatly shrunken. Their 

 outlines show that they are compressed as if between adjacent fibers. The fibrillar 

 structure has likewise disappeared. Slight vacuoles are present. The most diagnostic 

 feature of the change consists in the pigment granules of muscular atrophy. These 

 pigment granules are irregularly placed and vary greatly in size. Measured with the 

 1/12 oil immersion they vary between o.i and 0.2 /( in diameter. The degenerative 

 changes noted are typical of simple atrophy. The changes in this particular muscle 

 are the most advanced that have been noted. There is some slight indication of atrophy 

 in the trunk musculature even at an earlier stage of the journey, but nowhere else have 

 I found definite degenerative pigments, unless the highly refractive bodies noted in 

 no. 125 and no. 139 be such. 



The further details of these degenerative changes are being studied and will be 

 presented later in a special report. 



ANALYTICAL DETERMINATIONS OF THE PERCENTAGE OF FATS IN THE SPAWNING SALMON. 



The three Cazadero salmon of this series from which samples were taken for fat 

 percentage determinations reveal a larger per cent of fat than one would, a priori, expect. 



