290 Papers from the Department of Marine Biology. 



DESCRIPTION OF ILLUSTRATIONS. 



FIG. IA. Transverse section of 5 adjacent skeletal-muscle fibers (abdominal-spine muscles), 

 showing the great variation in diameter and the random distribution of the nuclei (n). X750. 

 Flemming's fixation; iron-hematoxylin stain. 



FIG. IB. More highly magnified portion (x) of the largest fiber shown in A. n, nucleus; 

 s, sarcolemma; p, perimysium (endomysium). The myofibrils are arranged in bundles 

 throughout the sarcoplasm and show a peripheral radial and a central vertical (paratan- 

 gential) division. X2.000. 



FIG. 2. Longitudinal sections of: (A) Contracted fiber; (B) uncontracted fiber. Z, telo- 

 phragma; Q, anisotropic disk; J, isotropic disk. X2.000. 



FIG. 3. Portions of longitudinal sections of muscle-fibers showing a smaller (.4) and larger (B) 

 nucleus. The perinuclear sarcoplasm contains fine lighter and coarse darker (g) spherical 

 lipoid granules. The telophragma (Z) is continuous with the nuclear wall, which projects 

 into a series of spines at the points of union. X2,000. 



FIG. 4. Striped-muscle fiber which has suffered distortion. The lines of distortion are identical 

 with the telophragmata (Z), demonstrating the attachment of the myofibrils to the ground 

 membrane. The myofibrils stain more intensely and are slightly swollen, giving a granular 

 appearance at this level, at the point of attachment to the telophragma. S, sarcolemma. 

 X2.000. 



FIG. 5. Portion of longitudinal section of skeletal-muscle fiber showing the telophragmata 

 (T) continuous with the sarcolemma. E, endomysium; M, myofibril; S, sarcolemma. 

 X2.000. 



FIG. GA. Transverse section of a large trabecula of cardiac muscle, showing the division into 

 several larger and a number of smaller branches. The trabecula and branches are enveloped 

 by a sarcolemma (S) in intimate association with the endomysium (E). The nuclei are 

 scattered promiscuously throughout the diameter of the fiber. XI, 000. 



FIG. 6s. More highly magnified portion (.T) of A, showing arrangement of myofibrillse into 

 lamellar and cylindrical groupings. X2,000. 



FIG. 7. Transverse section of small cardiac-muscle trabecula, showing the disposition of the 

 larger bundles (M) of myofibrils (in which the fibrillse are grouped in lamellae and cylinders), 

 the enveloping finely granular, delicate sacroplasm, and the confining delicate sarcolemma (S). 

 The nucleus in this section is peripherally placed. X2,000. 



FIG. 8. Portion of longitudinal section of cardiac-muscle trabecula. The telophragmata are 

 continuous with the sarcolemma (S) which is festooned between the membranes. That 

 portion of the membrane to which the myofibrils are attached is granular in appearance; 

 the extra fibrillar portion is non-granular. The sarcoplasm is finely granular. The endo- 

 mysium (E) is very intimately attached to the sarcolemma, but with picric acid-fuchsin 

 counterstain it stains red, while the sarcolemma remains unstained. When the action of 

 the stain is prolonged, endomysium, telophragma, sarcoplasm, and sarcolemma all take on 

 a red or pink color. X2,000. Zimmermann's fixation; iron-hematoxylin, with picric acid- 

 fuchsin counterstain. 



FIG. 9. Fiber in the uncontracted condition, showing the Z, Q, and J lines. X2.000. 



FIG. 10. Fiber showing the relationship of the telophragmata and the endomysium (E) to the 

 sarcolemma (S). The endomysium is red in color, while the sarcolemma and telophragmata 

 remain dark brown or black, in successfully acid-fuchsin stained preparations. X2.000. 



FIG. 11. Cardiac fiber in the uncontracted condition, showing the deeper-staining granular 

 modification of the myofibrillse at the levels of attachment to the telophragmata. A periph- 

 eral nucleus and the sarcolemma (S) are also shown. X2.000. 



FIG. 12. Heart-muscle nuclei (A and B) showing the relationship of the telophragmata to the 

 nuclear wall. The perinuclear sarcoplasm is bounded by fibrilla?; there is no indication of 

 a cell-membrane. The nuclear wall projects into spines at the points where the ground- 

 membranes are attached. X2.000. 



FIG. 13. Two adjacent cardiac fibers with intervening connective tissue (c. t., endomysium). 

 R, uncontracted fiber; C, contracted fiber; S, sarcolemma; b. c., blood-cell. Note the difference 

 in size and structure between the nuclei of the connective tissue and the muscle tissue. Both 

 connective-tissue cytoplasm and the perinuclear sarcoplasm contain lipoid spherules. 

 X2.000. 



FIG. 14. Multinucleated sarcoplasmic area. The division process is amitotic. X2,000. 



FIG. 15. Intercalated disk of cardiac-muscle fiber of Limulus, dividing a contracted (upper) 

 portion from an uncontracted (lower) portion. X2.000. 



FIG. 16. Diagrams to illustrate the probable derivation of the complex serrated type of inter- 

 calated disk characteristic of hypertrophied muscle from the simple-comb type by process 

 of longitudinal splitting of the myofibrils and unequal tensions among adjacent fibrils. The 

 myofibrils are numbered 1 to 5; Z, telophragma; d, intercalated disk, (A) comb type, 

 (B) type found sparingly in mammalian hearts, and exclusively in hypertrophied hearts. 

 The distortions suffered by the successive telophragmata adjacent to the one directly involved 

 in the disk are not taken into account in the diagram B. 



