i ORGANISATION AND STRUCTURE OF MUSCLE 35 



Sometimes the sarcoplasm will be found only in the centre of 

 the fibre, densely heaped up in a round, or slit-like, cavity. The 

 muscle-columns, which in such cases form broad bands, are set 

 radially round the central mass of nucleated protoplasm, like 

 the leaves of a book, separated only by very fine lamellae of 

 sarcoplasm, a disposition already familiar to us in the uni- 

 nuclear muscle -cells of many invertebrates. According to 

 Eollett, the direct transition to this most characteristic structure 

 in the muscles of the Dytiscidse is found in numerous little 

 Carabidas, e.g. Brachinus, and the common wasp, where the 

 muscle -fibres are more or less elongated in cross -section, and 

 present radially situated Cohnheim's areas in their longer 

 diameter. 



Eetzius (19) was the first to describe the very delicate trans- 

 verse figures exhibited by the muscle-fibres of Dytiscus marg. in 





righ 



^ 



b 



FIG. 25. a, Transverse section of muscle-fibres (extremities) of Dytiscus margincdis ; b, part of the 

 section on application of dilute acids. Small secondary strata denoting the cross-sections 

 of single fibrils appear between the primary strata of sarcoplasm. (v. Limbeck.) 



gold chloride preparations, to which we shall return presently (Fig. 

 25). But his interpretation of the figures (adopted later by Bremer, 

 v. Gehuchten, and Eamon y Cajal) must be regarded as fallacious, 

 chiefiy on the ground of the classical researches of Eollett. 

 Eetzius conceived the central muscle-nuclei with the surrounding 

 sarcoplasm to be true cells (analogous to Schultze's muscle- 

 corpuscles) with excessively fine processes, and believed that these 

 filiform nets, stretched horizontally in the muscle -fibre, were 

 arranged at regular intervals one beyond the other, the fibrils 

 lying in their meshes. On this assumption, the outlines of 

 Cohnheim's are?e, whatever their individual shape, must be viewed 

 not as the optical expression of the sarcoplasm accumulated at 

 the edges of the muscle-columns, forming a network of partitions 

 right along the muscle-fibres, but as the superficial aspect of the 



