86 BULLETIN OF THE BUREAU OF FISHERIES. 



smaller fibers and occasionally a medium-sized one which show a trace of fat around the superficial 

 ring of protoplasm. Such fibers are surrounded with fat droplets massed on the surface of the fibers 

 in tlie connective tissue. Some droplets are imdoubtedly under the sarcolemma. It is this fat which 

 gives the show of color at the superficial coat of fibrillae. In the smallest fibers of the section some 

 scattered liposomes of minute size are present between the fibrillse of the surface of the fiber. 



A longitudinal section of pink-trunk muscle (slide H8i) shows numerous fat droplets of com- 

 paratively small size adherent to the surface of the fibers. The sarcoplasm shows the striations in 

 splendid contrast, but no liposomes were to be found within the fiber. 



The intermediate zone of pink fibers. — The line of separation between tlie pink and the dark trunk 

 muscle is marked by a connective tissue septum. Occasionally a microscopic group of small fibers 

 may be found on the dark-muscle side of the septum (sec. H82). These intermediate pink-muscle 

 fibers have in their protoplasm a fe%v liposomes, which are limited to the small fibers. There is not 

 so broad a zone of intermediate fibers as was noted in the young muscle — for example, protocol no. 97. 

 Well out in the field of pink fibers of section HS2 there is an abundance of intercellular fat, but no 

 evidence of intracellular fat. 



Notwithstanding these exceptions, the general picture is that of muscle free from intracellular fat. 



Microscopic examination of the trunk dark muscle of fish no. 75 (section H"o). — Observation with 

 one-twelfth oil immersion. The section shows an abundance of fat both between the fibers and within 

 the fibers. The fat between the fibers is in droplets from 6 to 10 /( in diameter. The muscle fibers 

 themselves are only from 25 to 50 /i in diameter and somewhat irregular in outline. The fat droplets 

 are rather uniformly distributed among these fibers, though not so great in amount as in the same 

 type of muscle from Ilwaco. 



The intramuscular fat is present in large amount and very uniformly distributed through the 

 protoplasm of the fibers. The droplets, strictly within the fiber, vary around 4 /( in diameter. 



It is difficult to determine whether the fat droplets around the superficial zone are under the 

 sarcolemma, and tlierefore intracellular, or lie outside this membrane. Certainly in a number of 

 cases the former is the fact. In comparison with the dark muscle of the younger fish it is noted that 

 the intracellular droplets of the Monterey muscle are more uniformly distributed through the pro- 

 toplasm and have a more tmiform size. 



The intermuscular fat of the dark muscle of fish no. 76 (sec. H73) is in relatively large drops, jo/k 

 on an average in diameter; but there is only a small proportion of the intercellular fat present in 

 the finer droplets. The intracellular fat is rather uniformly distributed through the sarcoplasm; but 

 the droplets are smaller than in iish no. 75, 2 /<, or slightly larger, in diameter. 



VARIATION OF THE AMOUNT OF FAT IN THE SALMON DURING THE SPAWNING 



MIGRATION. 



It is to be expected that the amount of fat present in different portions of the 

 musculature of the salmon will vary sharply at different times during the migration. 

 Whether this variation will be directly proport'ional to the time since the migration 

 began remains to be discovered. The attempt in this paper is to present the normal 

 distribution of fats at the end of the feeding period — i. e., the beginning of the migration 

 phase — and to follow the variations through four typical regions of the Columbia River 

 Basin. The regions chosen represent (i) the tidewater stage of the migration, (2) an 

 early intermediate stage in the migration, (3) a later intermediate stage, and (4) the 

 condition at the spawning ground and at the time of death. 



As representing an early stage I have chosen a station at Ilwaco on the Washington 

 side of the mouth of the Columbia River. At this point P. J. McGowan & Sons have 

 a canning establishment, the lowest on the river. It is in the midst of the Bakers Bay 

 field of traps and is the most accessible point to the lowest channel fishing done on the 

 Columbia River. 



For the second stage Warrendale, Oreg,, about 6 miles below the cascades in the 

 canyon of the Columbia, was chosen. The upriver cannery of P. J. McGowan & Sons 



