446 J. GRAHAM KKKh'. 



of this work^ — which has been excised from the egg and laid 

 out in one plane while still alive, and then treated with the 

 fixing agent, it is found that the myotomes have been pulled 

 slightly away from the neural cord, and now the nerve-root 

 is quite visible (of. fig. 12 a) as a pale strand passing from 

 the neural cord near its ventro-lateral angle, outwards to 

 the inner surface of the myotome. At this period of develop- 

 ment (Stage 24) there are scarcely any mesenchyma cells 

 between myotome and spinal cord. Where occasionally such 

 a cell appears it is heavily laden with yolk granules, and is 

 by that easily distinguishable from the pale nerve-root. 



As development progresses the myotome recedes from the 

 neural canal with the development of mesenchymatous con- 

 nective tissue between the two, and the nerve-trunk is corre- 

 spondingly stretched out, or, to put it more correctly, it grows 

 in length accordingly. 



By Stage 27 (fig. 12 b) the nerve-trunk shows a very dis- 

 tinct fibrillation, and at its outer end its fibrils radiate out in 

 a beautiful cone-like manner over the inner face of the myo- 

 tome. In the middle of the cone the fibres are seen to pass 

 directly into the protoplasm, and the whole arrangement of 

 nervous tails to the muscle-cells, the latter having at this 

 stage developed contractile fibrils in the protoplasm adjoining 

 their three surfaces, dorsal, ventral, and external, irresistibly 

 calls to mind the nerve-muscle arrangements of the nematode 

 worms. Outside the conical arrangement of fibres mentioned 

 1 have not been able to demonstrate the connection of muscle- 

 cell with nerve-root, though of course there can be little 

 doubt that a similar relation holds. In all probability every 

 muscle-cell in the myotome passes at its inner end into a 

 nervous tail, but these are only conspicuous where they pass 

 away from the inner sui'face of the myotome at a considerable 

 angle ; over the greater part of the surface they are lying 

 closely apposed to it, and are hence difficult to see. 



As the mesenchymatous reticulum increases in quantity 

 between the myotome and the spinal cord its protoplasm (and 

 ' ' I'liil. Trans.,' vol. cxcii, Ji. 



