422 



arrange themselves in the form of five columns of cells, each 

 four cells in thickness. This condition of the bands is seen 

 in fig. 131. The cells now appear to lose their inner walls 

 so that five syncytial columns are produced, on the periphery 

 of which the nuclei are disposed ; other cells become incor- 

 porated later (see fig. 134). To these columns other myoblasts 

 now apply themselves; these, however, do not become merged 

 into the syncytium. On the contrary, retaining their cell 

 walls, they may be observed to give off at either end a pro€ess 

 (fig. 139). These processes grow right along the syncytial 

 mass and are the embryonic sarcostyles of which the adult 

 muscle contains so many. Shortly after the process can be 

 first observed the five syncytial columns begin to show a 

 very distinct fibrillated appearance, as more and more myo- 

 blasts, applying themselves to the columns, send their fibre- 

 like extensions into them. 



The process takes place with considerable rapidity, and 



already in the pupa four hours old the myoblast bands of the 



late larva now consist each of five columns of fibres (sarco- 



^ styles), surrounding each of which is the layer of cells from 



each of which a single fibre has been formed (fig. 134). 



Between the myoblasts in the early pupa curious heavily 

 staining rod-like structures may be observed (x in fig. 135). I 

 am unable to say what their significance is. 



The myoblast cells continue to multiply in karyokinesis, 

 and the strips grow considerably in breadth and thickness. 



Then, in the pupa about twelve hours of age, the two 

 bands at last split up into their five parts, and these are the 

 rudiments of the great longitudinal thoracic muscles (wing 

 muscles) of the imago. Each muscle consists, at this stage, of 

 a great number (between 800 and 900) of fibres, while an actual 

 count of the myoblasts surrounding it, really quite a simple 

 procedure, showed, in the same muscle, 871 of these to be 

 present. This fact, together with the observation of their 

 mode of development, can leave no doubt that the muscle 

 is built up of great numbers of fibres, each developed from 

 one cell, and not of innumerable fibrillae, as is usually sup- 

 posed. Between the fibres lies the interstitial substance, 

 formed, it would seem, from the five syncytial columns of the 

 early myoblastic bands. 



In the thirty-six hour pupa the muscle is still in almost 

 the same condition as that just described. The cells have 

 now, however, lost most of their walls, and, their outer walls 

 alone persisting, these form a structure which is comparable 

 with the sarcolemma of other types of muscle. So far as I could 

 observe, the connection between the nuclei and sarcostyles, 

 which must once have existed, disappears entirely, so that 



