402 



The muscles are covered with a very prominent sarco- 

 lemma. 



Tlie nuclei are three to five in number; they are round 

 or oval flat discs ; a very large nucleolus is usually present in 

 the nuclei of the fully-grown larvae ; or two nucleoli may be 

 present; a karysome is quite absent and the chromatin is 

 scattered in small granules throughout the nucleus (fig. 102a). 

 The nuclei, if round, measure about 17/x in diameter; if oval, 

 19-20^ in length, 13-14/x in breadth. The breadth of the 

 muscle is about 34^ ; the length varies apparently according 

 to the number of cells which entered ihto its formation; on 

 an average the muscles measure about 250/x, so that the length 

 of the individual ''cell" composing the syncytium is 63jul. 



The oblique muscles possess four nuclei; in their middle 

 they show a long slit, indicating the double origin of this 

 part. Their minute structure does not differ from that of 

 the longitudinal muscles. 



If the muscles of young larvae be examined, the essenti- 

 ally multicellular nature of the muscle fibres is clearly seen 

 (fig. 100). Three to five cells may be present arranged end 

 on end, and the cell boundaries are still unmistakable. In 

 the earliest stage (twelve-hour larva) in which I have 

 examined them they show distinct longitudinal fibrillation, 

 the fibrillae of successive cells in the developing syncytium 

 already fusing. Moreover, fibrillae from one fibre have already 

 communicated with those of others of the muscle band. 

 Striations are just beginning to appear; in some they are 

 distinctly visible, in others quite absent. The individual 

 cells measure 14/i. in length, 11|jia in breadth. The nuclei 

 are relatively gigantic and measure 12-14/x long by 8-9jul broad. 

 Nucleoli are quite absent; one or more small karyosomes 

 may be present, but a considerable part of the chromatin 

 may be scattered in granules throughout the nucleoplasm 

 (fig. 102b). 



Already at this stage, too, the connecting pieces can be 

 clearly seen between the adjacent muscle bands. In the 

 oblique muscles the four-celled condition is especially clearly 

 seen (fig. 99). 



The muscles grow rapidly; already in the second instar 

 the cell limits are scarcely visible. From now on the muscles 

 begin to differentiate into the condition in which we see them 

 in the adult. The process consists mainly in a special develop- 

 ment of the striations, and a general "loosening" of the 

 texture of the whole muscle by the development, apparently, 

 of more interstitial substance. The nuclei grow considerably 

 in size, hut the actual chromatin does not appear to increase 



4 



