THE MUSCLES AND NERVES. 287 



Most of the appearances which have been described in 

 striated muscle fibres are, I beheve, diffraction phenomena 

 arising from the super-position of many layers of sarcomeres ; 

 others arise from the coagulation of the sarcoplasm, or inter- 

 mediate substance. To the first I attribute the bright dots and 

 dark transverse lines, and to the latter the cracks which are seen 

 in transverse sections, and the reticulated appearances described 

 by C. F. Marshall in specimens prepared with gold chloride.* 



The development of the ordinary Skeletal Muscles, 'leg muscles,' 

 of the imago is readily observed in the nymph and immature 

 imago, and throws much light on the nature of the muscle 

 fibrillae. In the youngest state each fibre appears as a row of 

 cells placed end to end. In some cases the cells are fused 

 together into a multinucleated protoplasmic cord ; there is 

 at this period no trace of transverse striation. At a later 

 stage the nuclei exhibit karyokinetic figures, and divide in a 

 plane transverse to the fibre. A bright line, a cell plate, 

 appears between the two demiasters into which the nucleus 

 separates (PI. XVII., Fig. 7). The fibre increases in breadth 

 during this process, but the distance between the cell plates 

 diminishes with each division. Fibrillae next appear at the 

 periphery of the fibre. The cell plates are Krause's mem- 

 branes, and form the isotropous cement material of the 

 fibrillar, the cell substance between the plates being differ- 

 entiated into sarcomeres ; a portion remains undifferentiated 

 in the centre of the fibre around the nuclei. 



The superficial portion of the cell forms a kind of sarco- 

 lemma, which is more firmly attached to the cell plates than to 

 the intervening material. The bulging of the peripheral 

 portion of the fibre from the imbibition of fluid, formerly 

 rehed on as demonstrating that the membranes of Krause are 

 true septa, is due to this fact. 



The membranes of Krause, my cell plates, are not per- 

 manent ; they disappear as plates, and are only represented 

 by the isotropous material of the sarcostyles in the fully 

 formed muscle. 



* Quart. Journ. of Microsc. Science, vol. xxviii., iSSS. 



