I04 BULLETIN OF THE BUREAU OF FISHERIES. 



Microscopic examination of the caudal dark muscle (L14 and i;). — This transverse section of the dark 

 muscle from the tail is quite well supplied with fat. I do not see fat droplets that are unquestionably 

 between the fibers, but groups of droplets that lie just under the sarcolemma were noticed, the largest 

 of which were 7 11 in diameter. 



The intramuscular fat is greatly less than that in the dark muscle of the portion of the body where 

 tlie largest liposomes measure 3.6/1 in diameter, but this larger size is rare. The largest of the liposomes 

 run about 2 /< in diameter. The smaller are from this size down to 0.3 u and less in diameter. Judging 

 from the intensity of the stain, one would say that the caudal dark does not contain more than one- 

 fourth, possibly one-third, as much fat as tlie trunk dark. 



There are areas, especially along certain septa, which have a strikingly less quantity of fat. This 

 appearance is associated with the more vascular areas. 



Female salmon (no. 122), length Sgo mm., iceight 8,g8o grams, taken at Warrcndale, August ly, igii. 



This was a good conditioned fish, takenat McGowan's seining grounds, i]4 miles below Warren- 

 dale. The weight of the ovaries was 6S0 grams, stomach quite small, appearing one-half degenerated. 



Microscopic examination of the trunk pink muscle (trans^'erse section, LjS). — This section shows a rela- 

 tively large quantity of fat between the fibers, not so much, however, as in no. 115 and no. 118 (1/12 oil 

 immersion). The larger drops measure about 20 /i in diameter. The distribution is similar to that in 

 the fish just mentioned. In this section the smallest fibers, 40 /i in diameter, are thickly set with lipo- 

 somes distributed rather uniformly through the fiber. These liposomes varj' in size from 0.6 to 1.3 /i 

 in diameter. In the medium fibers, 75 to 100 /< in diameter, the number of liposomes diminishes in the 

 center of the fiber; also there is a marked diminution of the size of those present. In one fiber, 100 n 

 in diameter, the liposomes in the middle of the cross section measure from o.i to 0.4 /i in diameter. 



In the larger fibers of the section, those above 100 /( in diameter, there is a marked diminution of 

 liposomes. This diminution is most apparent in the main body of the fiber, i. e., exclusive of the super- 

 ficial area. This contrast in amount of liposomes between the deep and superficial part of the fiber 

 is sharp, giving the fiber the appearance in cross section of having a superficial ring of fat. In certain 

 of the larger fibers, the central liposomes are absent, or, at any rate, one can not distinguish tliem with 

 the oil immersion. In tliese same fibers liposomes around the superficial border will vary greatly in 

 size, measuring from scarcely identifiable liposomes up to as much as 1.4 /i in diameter. 



An examination of the longitudinal sections (L33), brings out the fact that there is a relatively 

 high content of fat near the surface of the fiber, both external to the fiber and just under the surface. 

 The external fat is in the connective tissue, the endomysiura, therefore, intermuscular. 



Microscopic examination of the cattdal pink muscle {section Ljl). — The fibers are almost free of fat. 

 There is no intermuscular fat hanging to them, but the connective tissue, myocommata, of the caudal 

 pink muscle (slide Ls4) is crowded with adipose fat. 



Scattered over the surface of the fiber, all apparently under the sarcolemma, is a good deal of fat 

 in droplets, from 2 to 3 /i in diameter, not uniform in size. The small and intermediate sized fibers have 

 tolerably evenly distributed chains of smallest liposomes. In the larger fibers the central portion is 

 relatively free of chains of liposomes, which, in many instances less than 0.2 /i in diameter, are so small 

 they are difficult to identify. Certain of these teased fibers show the striations clearly. In one such 

 example there are 13 striations in 36/1 (slide L54, i5striation to 36/)). The diameter of the fiber showing 

 these striations is 63 /j. The chains of finest liposomes in the largest fibers are not always perfect. The 

 irregularity is due to the dropping out of individual liposomes. In some chains there are more liposomes 

 than fibrillae. This is due to the presence of two liposomes in the space opposite certain striations. 

 There is not always perfect correspondence in the number of striations and liposomes in the chains in 

 these pink fibers. 



This slide gives examples of tlie cone-like ends of the fibers. These ends are supplied with lipo- 

 somes just as in the body of the fiber. All the teased material of the caudal pink fibers shows an increased 

 quantity of fat at the surface of the fiber. This fat is in tiny droplets varj'ing from the smaller liposomes 

 0.2 /I in diameter up to 2.5 and even 3 /i. Many of the droplets are in regular rows, but not so regular 

 as those deep in the muscle fiber. Undoubtedly this fat is just under the sarcolemma, a fact confirmed 

 by the appearance when the optical section cuts the middle of the fiber. 



Microscopic examination of the trunk dark muscle (sections Ll8-2^). — These transverse sections show 

 a relatively large quantity of intermuscular fat. The fibers are more widely separated than is usual 



