lOO BULLETIN OF THE BUREAU OF FISHERIES. 



an average for the station, however, one must say that the presence of liposomes is very 

 greatly reduced, both in size and number for all the int:;rmediate fibers, while for the 

 larger fibers it is present only in traces. 



Trunk dark muscle. — In the dark muscle of salmon from the Warrendale station 

 there is even wider variation as regards the loading of fat than in the pink muscle. In 

 fish nos. 1 20 and 121 the amount of fat in the trunk dark muscle is very great, while in 

 no. 125 it is low. In the fatter salmon the loading of fat is almost as great as in the 

 specimens from Ilwaco, with the exception of Ilwaco specimen no. 1 1 1 which was an 

 extraordinarily fat fish. On the other hand, in the poorer specimens the amount of dark 

 muscle fat is only a small percentage of that at the Ilwaco station. 



The intermuscular fat is comparatively plentiful, is located in the connective tissue 

 septa and in the myocommata. However, the fat droplets average much smaller in 

 size than in the Ilwaco specimens. Oftentimes the number of these fat droplets, espe- 

 cially of the smaller ones, seems relatively greater. In Warrendale fish the individual 

 fibers are usually somewhat more definitely separated and this fact makes it easier to 

 determine the relation of the intermuscular fat. In fish no. 125 the amount of this 

 intermuscular fat is very low, but occasionally individual drops are as large in this fish 

 as in those that have more fat. The amount of intermuscular fat varies in difi"erent 

 regions of one and the same muscle. This variation undoubtedly is associated with a 

 process of fat erosion which was first obser\'ed in certain Ilwaco specimens. In Warren- 

 dale fish the erosion process has gone much further and is more readily followed. In 

 areas in which the fat has been most fully eliminated the intermuscular fat is reduced 

 to tiny droplets. 



The intramuscular fat of the dark trunk muscle is abundant in all of the fibers of the 

 fatter fish. In no. 120 the cross sections and the teased preparations show that the 

 fibers are especially richly supplied with liposomes in their sarcoplasm. The liposomes 

 are of large size and in relatively long chains. There is considerable fusion of adjacent 

 liposomes. Especially in fish no. 121 the liposomes are so large that one might better 

 describe them as droplets. The diameters run from i to as much as 4,«. Certain of the 

 fibers in this fish and also in fish no. 122 show fusion of liposomes into long rods of fat. 

 These slender rods usually appear more or less constricted at points corresponding to the 

 striations of fibrillse. 



The most striking thing about the fat in the trunk dark muscle ol fish from the \\'ar- 

 rendale station is its great irregularity in different microscopic areas. This has been 

 spoken of in connection with the very fat fish no. 1 20, but it is an appearance that marks 

 every fish examined. If the specimen is one of low grade, as in no. 125, then these irregu- 

 larities are most prominent. Certain groups of dark muscle fibers will appear richly 

 loaded with fat while other areas will be almost free, certainly will not contain more than 

 from 30 to 50 per cent as much as in the fatter areas. In these clear areas the reduction 

 in fat is due to two factors: First, the great reduction in the average size of the liposomes; 

 and second, the great decrease in the number of liposomes. In numerous areas where 

 muscle fibers are in close contact with small blood vessels the fat is very low in amount. 

 This condition is described in the protocol of fish no. 125. The characteristic picture 

 presented where a group of fibers lies along the blood vessel is as follows : First, that por- 

 tion of the fiber next the blood vessel will have no intermuscular fat; second, the intra- 

 muscular fat will be either absent or greatly reduced in the corresponding area; third, 



