EXPLANATION OF FIGURES. 



Fid. 1. Cross-section of the entire mnscularis of the contracted large intes- 

 tine of (log — 1. m., longitudinal muscle ; c. m., circular muscle ; c. w., contraction 

 wave ; i. s., internodal segments of muscle fibers ; c, an oblique contraction 

 wave. Zenker's fluid. Iron-haematoxylin. X 390. 



Fig. 2. Longitudinal section of a group of muscle fibers from the muscular 

 stomach of chicken showing a portion of a contraction wave (c. w. ) with 

 uncontracted areas on either side. The enlargement of the muscle fibers in 

 the contraction wave is marked. In the contraction wave (c. w.) the con- 

 traction nodes (c. n.) appear homogeneous and are stained very deeply. In 

 the uncontracted areas the internodal segments (i. s.) are fibrillated and 

 lightly staining — i. c, interstitial connective tissue; f. mf., fine myofibrillse; 

 r. nu., an elongated resting nucleus. Zenker's fluid. Iron-h;iematoxy]in. 

 X 1275. 



Fig. 3. Cross-section of a portion of the circular muscle coat of the con- 

 tracted large intestine of dog. This section shows plainly the enlargement 

 and deep staining of the muscle fibers at the contraction nodes (c. n.) as 

 compared with the uncontracted internodal segments (i. s.). The myofibrillse 

 In the internodal segments are only indistinctly shown — i. c, interstitial con- 

 nective tissue. Zenker's fluid. Iron-haematoxylin. X 2250. 



Fig. 4. Cross-section of a portion of the media of the contracted carotid of 

 ox. c. n., contraction node. The contraction nodes in this section are distinctly 

 fibrillated. In them the cut ends of the coarse myofibrillse are shown, c. mf. 

 In some of the .fibers not firmly contracted (d.) both coarse and fine myo- 

 fibrillfe (f. mf.) appear — i. s., either an entirely relaxed fiber or an inter- 

 nodal segment of a contracted fiber ; i. c. interstitial connective tissue ; r. nu., 

 resting nucleus : c. nu., contracted nucleus. Zenker's fluid. Iron-hfematoxylin. 

 X 1650. 



Fig. 5. Longitudinal section of a portion of a contracted muscle fiber from 

 the media of the carotid of ox, showing two contraction nodes (c. n.) — i. s., 

 internodal segment ; r. nu.. resting nucleus ; c. mf., coarse myofibrillfe. Zenker's 

 fluid. Iron-bfematoxylin. x 1650. 



Fig. 0. Section of a portion of a partially contracted muscle flber from the 

 intestine of Necturus, showing the continuity of the myofibrilljie through the 

 contraction nodes (c. na. and c. nb.). The enlargement of the myofibrillne is 

 shown in contraction node c. nb. This cell has only fine myofibrillje — g. p., 

 granular protoplasm; f. mf., fine myofibrillse; c. f., collagenous fibers; c. n. b., 

 a contraction node just beginning to form ; c. n. a., a more firmly contracted 

 node. Zenker's fluid. Iron-ha?matoxylin. x 2250. 



Fig. 7. Cross-section of a small portion of the circlar muscle coat of 

 Necturus taken near the submucosa, showing the continuity of both granular 

 protoplasm and myofibrillje from cell to cell. The tissue is a complete 

 syncytium — g. p., granular protoplasm ; f. mf., fine myofibrillje. Zenker's fluid. 

 Iron-h:ematoxylin. x 22.50. 



(Continued on next page.) 



