THE MUSCLES AND NERVES. 283 



brates. Except in being colourless, they closely resemble the 

 pale muscle fibres of Mammals. 



The ordinary or leg muscles in the imago exhibit no proper 

 sarcolemma, and have their nuclei arranged in the centre of 

 the fibres. Their transverse striae are more marked than in 

 the muscles of the larva, and the fibres frequently exhibit the 

 appearance of being divided into ' muscle cases ' by transverse 

 septa ' Krause's membranes.' 



Each muscle consists of one or many fibres, either inserted 

 in a bundle into a common apodeme, or on one or both sides of 

 the apodeme in a penniforrn or bipenniform manner. More 

 rarely the fibres are inserted into the integument through the 

 medium of fibrillated hypodermal cells, which closely resemble 

 tendons (PL XVII., Fig. 5, 6). 



The wing muscles, sternodorsales and dorsales, are softer than 

 the ordinary muscles. Each consists of several giant fibres 

 without any sarcolemma, but surrounded by tracheal vessels 

 and epithelioid cells. Each fibre consists of numerous fasciculi 

 of fibrillse, separated from each other by numerous nuclei. 

 The fibres are easily broken up into their constituent fibrillas, 

 and only exhibit the faintest indications of transverse striation. 

 Leydig [123] described the wing muscles of Dytiscus as yellow, 

 possessing but little solidity, and as very easily separated into 

 their constituent fibrilise. In the fresh condition the wing- 

 muscles of the Blow-fly are so soft that they appear almost 

 semi-fluid. They have a bluish-gray colour. 



The Visceral Muscles of the Blow-fly are distinctly striated ; 

 those of the alimentary canal consist of fusiform (often 

 branched) flattened cells, with a single large ovoid nucleus 

 embedded in each cell. These cells are united into fenestrated 

 laminae by an intercellular cement substance, and, except that 

 they exhibit very distinct transverse striae, they bear a close 

 resemblance to non-striated muscle fibre. 



The muscle fibres of the dorsal vessel differ entirely from 

 those of the alimentary canal. The dorsal vessel consists of a 

 muscular tube formed of very fine transversely striated fibrillae, 

 which branch and form a longitudinal network around the 



