MUSCULAR TISSUE. 181 
4. The muscular tissue of the crayfish always has the 
form of bands or fibres, of very various thickness, marked, 
when viewed by transmitted light, by alternate darker and 
Fig. 52.—Astacus fluviatilis.—A, « single muscular fibre, transverse 
diameter ;1;th of an inch; B, a portion of the same more highly 
magnified ; C,a smaller portion treated with alcohol and acetic 
acid still more highly magnified ; D and E, the splitting up of a 
part of a fibre, treated with picro-carmine, into fibrille; F, the 
connection of » nervous with a muscular fibre which has been 
treated with alcohol and acetic acid. a, darker, and 0, clearer portions 
of the fibrille ; 2, nuclei ; nv, nerve fibre ; s, sarcolemma ; ¢, tendon ; 
- 1—5, successive dark granular strize answering to the granular 
portions, a, of each fibrilla. 
