Io6 BULLETIN OF THE BUREAU OF FISHERIES. 



The fibers are thickly studded with chains of liposomes 0.6 to 2 ju in diameter. Only occasionally 

 are adjacent liposomes fused as in no. 121 and no. 122. The longitudinal section shows a greater 

 quantity of fat along the borders than in the bodies of the fibers. 



The fat under the sarcolemma is in drops measuring from 4 to 5 /t in diameter, occasionally 6 /i. 

 The number of these fat droplets around any given fiber varies greatly, due to the fact that the fat is 

 being removed in the neighborhood. Choosing an area containing the most fat, the intramuscular fat 

 is in liposomes from 0.4 /i in diameter up to as much as 4.3 ji. The number of the largest droplets is 

 relatively small, but when present they are evenly distributed through the fiber. There is great 

 variation in the size of the liposomes in different portions of the length of one and the same teased 

 fiber. 



In the areas referred to above the intramuscular fat is reduced in amount. The size of liposomes 

 is affected more than the number of chains. There are several fields through which small blood vessels 

 go in which that portion of the muscle in contact with the blood vessel is strikingh- free of fat. In the 

 neighborhood of a blood vessel where the fat is most removed the droplets lying under the sarcolemma 

 are reduced to a few liposomes lying on the side farther from the vascular area. The largest of these 

 liposomes measure 1.6 p. in diameter. Through the body of the same fiber in the half opposite the 

 blood vessels the liposomes are fewer in number and relatively smaller in diameter (0.4 to i fi) than 

 in portions of the fiber not in contact with blood vessels. In the third of the muscle lying next to the 

 vascular area the liposomes are still present, but small — too small to measure accurately. There are 

 numerous areas in this section (L74) showing contrast as regards the degree of removal of fat. 



Microscopic examination of the caudal dark muscle. — There is quite a little fat in the myocommata. 

 Through the body of the dark muscle, however, there is no intermuscular fat. 



Under the oil immersion certain fibers of this section are absolutely clear of fat within the fiber. 

 In other fibers there are traces of liposomes too small to measure. These traces are confirmed by fibers 

 which have been turned to a horizontal position in the handling. In still other fibers there are scattered 

 and irregularly placed groups of liposomes at points near the surface, but none deep down in the sub- 

 stance of the sarcoplasm. The fattest fibers observed contained a fairly uniform sprinkling of liposomes 

 around the superficial area of the fiber and a somewhat smaller quantity in the middle of the fiber. The 

 whole preparation presents as nearly a fat-free section as has been observed of caudal dark muscle. 



A number of fibers contain numerous spherical bodies measuring approximately 2 /x in diameter 

 and having a dark-red color (1/12 oil immersion). These bodie are irregularly placed through the 

 substance of the fiber, as are the brown pigment granules of degeneration. The stained bodies are 

 spherical, and one might take them for fat bodies. However, if they are fat bodies then the color of the 

 stain is distinctly different from the type. This color is a brilliant dark neutral red as against the usual 

 lighter brick red characteristic of this stain. It is possible that we are dealing here with the reaction 

 of some special fat which stains differentially, according to the obser\-ations of Eell. 



Female salmon (no. 126), length ~So mm., weight not taken, Warrendale, Columbia River, August 24, igil. 



This salmon was fresh from the McGowan seining ground and was chosen as representative of the 

 group of fish which show an advanced stage of migration change at this station. 



Microscopic examination of tlie trunk pink muscle (tratisverse sections i^Il-j, L/8). — The intermuscular 

 fat is in relatively small amount. The myocommata contain a small amount of fat arranged as a narrow 

 band of droplets on either side of the tendon. The larger fat drops measure 30 to 40 ,u in diameter, seldom 

 more. The intermuscular septa still contain a small amount of intermuscular fat. In the larger of 

 these sheets of connective tissue a few fat droplets measure as much as 15 /i in diameter, most of them 

 less. These are in the areas where in fish no. i iS the droplets were as much as 100 /jl in diameter. Most 

 of the fat drops are small and in relatively small group of 9 or 10 droplets in a group. 



The intramuscular fat is very low in this specimen. It is present in the small_ and intermediate 

 fibers, but difficult to distinguish in the larger fibers. The smallest fibers have tlieir intracellular fat 

 tolerably thickly sprinkled over the microscopic field. Most of these fibers show a somewhat greater 

 amount of liposomes near the surface. The medium fibers show great variation. Certain ones are 

 almost clear of liposomes, while others have a liberal sprinkling. In muscles of this size there is a con- 

 densation of fine liposomes under the sarcolemma. The same arrangement is true for the smallest fibers. 

 These small intracellular liposomes are 0.4 to 0.6 /( in diameter. 



