82 HISTOLOGY 



slightly elongate, larger than the average nucleus in other tissues of the 

 sucker, and have a single or double nucleolus of large size that stains 

 jet black in this specimen. The nucleoli lie in the longer axis of the 

 nucleus, and the caryoplasm is clear, owing to the small amount of the 

 chromatin which gathers into a few dense masses near the nuclear 

 membrane. 



The nuclei are fairly numerous and generally lie in the cytoplasm 

 between the fibril bundles and the sarcolemma. They here form rows 

 that stretch for some distance in the fiber on its long axis. In addition 

 to these muscle nuclei lying outside the fibril bundles there are several 

 which lie inside or among the bundles. These are always placed close 

 to the extreme end of the fiber, near the septum of the myotome, and the 

 fibrillae part to pass on each side of them, leaving a long cone-shaped 

 space at each end which is occupied by sarcoplasm. The sarcoplasm 

 is remarkable for its granular rather than its reticular appearance. 

 This is due to the large number of granules, the myochondria, which 

 lie in irregular masses in an otherwise typical cytoplasm. 



A delicate lax connective tissue is found throughout the mass of 

 muscle fibers. Its individual cells, whose outlines are irregular and 

 indeterminate, possess nuclei which are characteristic, being thin and 

 flat and round, or elongated into an oval form. They are smaller than 

 the muscle nuclei and possess a denser caryoplasm, which contains more 

 chromatin. The nucleolus is multiple and its several very small parts 

 are distributed around the periphery of the nucleus rather than in 

 the center. 



Such portions of this network of connective tissue as come in contact 

 with the cell body of a muscle fiber, form a layer that covers every part 

 of the fiber's surface and is so intimately connected with the sarcolemma 

 that it cannot be separated from it. The true sarcolemma is a cell- wall 

 of homogeneous structure and of no great strength or substance. It 

 cannot be demonstrated apart from the connective- tissue layer which 

 surrounds and adheres to it. Such nuclei as are to be in the sarcolemma 

 belong, of course, to the connective- tissue elements. 



Blood capillaries, with their delicate endothelial walls and con- 

 tained red corpuscles, lie between nearly every two fibers. The nuclei 

 of their walls are almost identical in shape, size, and other features with 

 the connective-tissue nuclei. Blood plates are well demonstrated in 

 these capillaries. 



The bundle of fibrils next claims our attention. That this is com- 

 posed of real individual fibrils is indicated by its appearance and by the 

 fact that in the specimen we examine, some individual fibrils are sepa- 

 rated from their fellows and shown alone and in their integrity. 



Such a fibril is composed of two kinds of substance according to the 



