60 



MUSCULAR TISSUE. 



sented by the spongioplasm, and the clear substance by the hyalo- 

 plasm. When stimulated, 

 the clear substance passes 

 into the pores as the hyalo- 

 plasm does into the spongio- 

 plasm, thus producing con- 

 traction ; and in the absence 



FIG. 53. Diagrams of the transverse stria- 

 tion in the muscle of an arthropod ; to the 

 right with the objective above ; to the left 

 with the objective below its normal focal 

 distance (after Rollet, 85) : Q, transverse 

 disk; h, median disk (Hensen); E, terminal 

 disk (Merkel) ; N, accessory disk (Engel- 

 mann) ; J, isotropic substance (Bohm and 

 David off). 



FIG. 54. Cardiac muscle, 

 semidiagrammatic : a,, nu- 

 cleus; b, branch of fibers; c, 

 cross-striation . 



of stimulation it passes out, as in the case of the ameba, causing 

 in it the formation of pseudopodia, and in the muscle its extension. 



-- Nucleus 



Contractile 

 substance. 



FIG. 55. 



"Contractile 

 substance. 

 Nucleus. 



FIG. 56. 



Longitudinal and cross-section of muscle-fibers from the human myocardium, 

 hardened in alcohol; x640. The muscle-cells in the longitudinal section are not 

 sharply defined, and appear aspolynuclear fibers blending with one another : between 

 them lie, here and there, connective-tissue nuclei (Bohm and Davidoff). 



