Muscles of Body-zvall 



85 



terminate the body in certain Tipnla- larvae. In other 

 hxrvae they are often reduced, and instead of being dorsal, 

 lateral, and ventral, one pair only may be retained. The 

 dorsal circumspiracular papillae may be two, four, or six 

 in number ^. One pair of these become large and fringed 

 with long setae in the aquatic larva of Pericoma, and 

 enclose the bubble of air which buoys up the taiP. In 

 the Dicranota- larva only the ventral pair are retained ; 

 these become long and apparently respiratory ^. Aquatic 

 Nemoceran larvae which have no open spiracles, such as 

 Chironomus, Tanypus, and Simulium, seem always to 

 want the circumspiracular papillae. 



Fig. S'- — Histology of larval muscles, i, subcutaneous larval muscle, showing 

 contractile columns (to left), and protoplasm with nuclei (to right). X 200. 

 2, transverse section of ditto, showing muscle-fibres enclosed in protoplasm. 

 X 125. 3, muscle-fibres, from body- wall, x 800. 4, ditto, from head. X8oo. 



7. The Bod //-wall, Blood-space, and Fatty Tissues. 

 The muscles of the body- wall, of the prothoracic and Muscles of 



"^ . , body-wall. 



anal feet, and of the head, are shown in figs. 19, 20, 30-36. 

 The muscles of the head and thorax are very different 

 in arrangement from those of the fiy, and are completely 

 renewed during the transformation. 



1 Osten Sacken, 1869, p. 7. In tlie blow-fly larva twelve small papillae 

 are found in the same situation. 



^ Miall and Walker, 1895. ' Miall, 1893. 



