507 



thoracic muscles which are beginning to lose their striations 

 and ultimately form the wing muscles. They penetrate the 

 muscles, which soon become riddled with these cells and 

 ultimately absorb them; in their place is formed a pair of 

 bands of myoblasts. Some of these myoblasts fuse in five 

 longitudinal columns within each band, and the syncytium 

 remains as the sarcoplasm of the future "wing muscles.'' 

 Other myoblasts send off processes into these columns and 

 form the sarcostyles of Schafer, which are therefore fibres, not 

 fibrils, as usually supposed. Each band then breaks up into 

 its five constituents, and the great ''wing" muscles of the 

 thorax are formed. The ''muscle insertions" are always 

 iutegumental cells. 



Other muscles of the larva, which may show all kinds of 

 disintegration processes, may become absorbed by leucocytes; 

 others, again, dissolve slowly in the blood stream, usually 

 throwing out large rounded globules as they do so. A specially 

 I remarkable case of disintegration is seen when the whole of 

 the minute sarcous elements are cast out as a fine shower of 

 "bacillus-like" rods into the blood stream where they dissolve 

 (fig. 104). 



In all cases the adult muscles are regenerated from 

 embryonic cells (myoblasts), like leucocytes in appearance, 

 which have lain dormant during larval life. They unite one 

 I after the other to form syncytial columns, one or more cells in 

 thickness. If more than one cell in thickness the columns 

 may (head, leg, and ovipositor muscles) or may not (pharyn- 

 geal dilators) become pulled apart to form a number of 

 narrower columns. Each of these columns undergoes fibrilla- 

 tion and striation by a method quite different from that 

 described in the "wing" muscles. In structure the muscles 

 always present striations in the form of double spirals. Certain 

 unicellular intestinal muscles may be markedly branched, each 

 branch consisting of only a few fibrials. Striation is here 

 truly transverse. 



E. The Irotestine. 



Tlie larval intestine consists of fore-, mid-, and hindguts. 

 The latter does not open into the midgut till towards the end 

 of larval life. This marks the defaecation period. 



The imaginal tissues are (1) a ring around the posterior 

 end of the oesophagus, (2) scattered cells at the bases of the 

 larval cells of the midgut, (3) cells surrounding the anterior 

 parts of the rectum. Salivaiy glands are well developed; 

 into the midgut open three hepatic caeca; malpighian tubes 

 are absent in the larva. 

 p2 



