232 B. MELLAND. 



(d) Crustacean. 



An exactly similar network can be brought out in the muscle 

 of the lobster. My friend Mr. C. F. Marshall has made prepara- 

 tions of lobster muscle with acetic acid and gold which show this 

 network in a most beautiful manner. The muscle in this case was 

 left in 15 per cent acetic acid for fifteen minutes (a much longer time 

 than I use), in gold chloride thirty minutes, and in 25 per cent formic 

 acid in a warm chamber for three hours exposed to the light. 



This network represents the transversely and longitudinally arranged 

 network described in insects' muscle pulled out of shape. In some of 

 the fibres indeed it is still seen arranged in the rectangular manner. 

 Fig. 8 represents a portion of a fibre in which transverse are crossed 

 by longitudinal lines with dots at the intersections. In this case the 

 ordinary light and dim transverse striation is obtained by refraction 

 round the nodal dots. 



At first sight the meshes of the irregular network described in the 

 frog and lobster look too large to correspond in size with the meshes of 

 the horizontal network in Dy tiscus, that is, with the end view of sarcous 

 elements. But we must not forget the effect of pressure ; it expands 

 the fibre to about ten times its normal diameter, and a corresponding 

 increase in the -size of the meshes takes place. Fig. 1 1 represents a 

 transverse section of the fibre of the frog cut fresh with the freezing- 

 microtome and stained by the gold method. It has not been much 

 enlarged by pressure, and hence the meshes of the network are small. 



Fig. 10 represents a portion of a fibre of the lobster which has split 

 into fibrils ; an uncommon effect in gold preparations. When muscle 

 splits into fibrils the fibres of the transverse network rupture midway 

 between the nodal points ; the longitudinal threads and dots remain 

 often attached to the fibril of sarcous substance, and cause it to appear 

 transversely striated. 



The muscular fibres of the crayfish show exactly the same network, 

 the precise method of gold staining seems to make little difference. 

 Isolated portions of network are seen pulled out of 'shape, and thus 

 with polyhedral meshes as in fig. 7. At other points the network is 

 seen still arranged in its typical manner as in fig. 8. 



(e) Rat. 

 In the Rat most of the fibres show the typical arrangement into 

 transverse and longitudinal portions (fig. 9). The transverse network 



