94 BULLETIN OP THE BUREAU OF FISHERIES. 



in diameter, rarely larger, as observed in a certain large fiber under examination. This fiber is 200 ^ 

 in diameter. The liposomic chains are comparatively imiform in their disposition throughout the 

 mass of the fiber. The liposomes themselves are not uniform in diameter in the rows. Adjacent droplets 

 may alternate between small and large sizes, though in some of the rows the droplets are fused, thus 

 making an oval droplet extending across the intervening striation membrane. In some of the smaller 

 muscle fibers the fusions are much more extensive , extending over four or five striations. In the smaller 

 fibers the fat droplets are relatively larger, averaging between 1.5 and 2 ;i in diameter. Over the surface 

 of the fibers and under the sarcolemma there is a sprinkling of small fat droplets from 2 to j ;( in diameter. 

 These are irregularly placed. 



The caudal pink muscle was not prepared in this fish. 



Trunk dark viuscle {longitudinal section, Ji). — The preparation is so filled with fat that the structure 

 is obscured . The intermuscular fat is in the largest drops observed for the trunk dark muscle , the average 

 diameter being about 30 /i. These drops are often compressed into oval outlines by the pressure of 

 the fibers. The muscle fibers themselves are only about 40 /t in diameter. 



There are large quantities of intramuscular fat, the droplets being simply crowded throughout the 

 whole structure. The larger intramuscular droplets are from 15 to 20/1 in diameter. These large droplets 

 often appear In rows along the course of the fiber, giving the appearance of splitting the fiber. However, 

 they only press the fibrillae apart. There are relatively few of the smallest liposomes present, though 

 the bundles of fibrillae all show a certain number of these small liposomes. The quantity of fat in this 

 preparation is the greatest for any dark muscle noted in the whole season's work. The droplets are 

 larger, relatively more numerous, and have so distorted the relations of the fibrillae as to break up the 

 regularity of the structure. 



Another section (J33), fixed 18 hours in formalin, gives a much better view of the outlines of the 

 fibers. The fibers are crowded thickly with relatively large intracellular droplets. They are so numer- 

 ous as to form almost a continuous layer of drops. A section (J35) stained in sudan shows the same 

 crowding of fat as those stained with scarlet red. The contrasts are less sharp. 



The myocommata of the tnmk dark muscle are filled with adipose cells which are crowded with 

 fat. Many of the cells have ruptured and the fat has run together, but the fat drops of those cells still 

 intact measure from 50 to 70 fi in diameter. 



Caudal dark muscle (transTjerse section, J20). — The dark muscle of the caudal peduncle is very fat, 

 but not so fat as in the trtmk muscle. The drops are relativel)- smaller. Those between the fibers 

 are from 6 to 15/1 in diameter. The fat within the fibers varies extremely in different parts of the section. 

 I notice one region in which the fibers are almost free of large drops of fat; only smaller liposomes are 

 present. In the near neighborhood of this group the fat is gathered around the siuiace of the fibers, 

 apparently just under the sarcolemma, where the drops vary from 5 /x down. The centers of these fibers 

 have liposomes averaging only about i /( in diameter. In that portion of the section which is fattest 

 the central portion of the fibers has larger droplets, not averaging more than 3 p., however. From this 

 section it seems that the caudal dark muscle must have a greatly reduced amount of fat in comparison with 

 the trunk region. Slide J21 shows relatively more fat than slide J20. The fibers are cut somewhat 

 obliquely, and this brings out the fact that the drops are oval in shape, as in the lateral line region. 



Intercostal muscle {longitudinal section, Jy). — This section has a large amount of intermuscular fat. 

 There are numerous large drops averaging 30 fi. The connective tissue of the whole section is jotted 

 full of very fine fat droplets, from i to lo/i. There is a trace only of intramuscular fat, nothing comparable 

 to that in the teased trunk muscle. This fat is in extremely fine liposomes, averaging only a fraction 

 of a micron in diameter. It seems quite imiformly distributed throughout the substance of the fibers. 



Muscles of the anal fin {transverse section, J2J and ji). — This section was across the group of muscles 

 between the interhemal spines and should therefore be of the erector and depressor muscles. There is 

 a small group of fibers on the outer margin of tlie section different from the main body, which probably 

 belongs to the inclinator muscle of the fin. 



There is a very small quantity of intermuscular fat. The drops are scattered but relatively large. 

 The main portion of the muscle has only traces of liposomic fat in extremely fine granules. There are 

 no rings of fat droplets under the sarcolemma of the type which characterizes fat-exhausted muscle. 



The group of fibers on tlie outer margin of the section has a tmiform distribution of intracellular fat 

 in comparatively large liposomes. These liposomes average 2 /t in diameter. They are quite evenly 

 distributed throughout the substance of the fiber and imder the sarcolemma, where they are somewhat 



