INTRODUCTORY REMARKS. 5 



differ in no important character from those of the highest 

 animals. The chief difference is seen in the larger size of the 

 gland cells. The muscular fibres are described as larger 

 than in vertebrates. This has probably arisen from the larva 

 and not the perfect insect, having been examined. All 

 the tissues in the larva, except the nerve cells and fibres, 

 are four or five times as large as in the perfect insect, but this 

 seems to depend rather upon rapidity of growth than upon 

 any inherent difference. 



The striated muscular fibre in the fly varies from 1 -3000th of an inch in 

 diameter in the muscles of the halteres and abdomen, to l-1000th in the 

 pharyngeal muscles and those of the legs, but in the larva several of the 

 muscles have fibres as large as 1 -200th of an inch in diameter. 



All the muscular fibres of the alimentary canal and dorsal vessel 

 exhibit striae. The only non-striated muscles I have been able to detect 

 are the great longitudinal dorsal muscles of the thorax ; these consist of 

 long clear fibres less than 1 -5000th of an inch in diameter, swollen at 

 intervals and containing nuclei. Numerous slightly granular cells lie 

 amongst them. No myolemma exists, although the tracheal vessels appear 

 to separate them into bundles ; so that they are soft aud easily broken 

 up into a mass of cells and fibres. 



Nuclei exist permanently in the myolemma of the striated muscles, and 

 appear in rows when they are treated with acetic acid. In many the fibres 

 branch, and the branches are as large as the primitive fibres. The muscles 

 of the abdomen and crop are flat bands of fibres with well marked striae ; 

 those of the crop terminate in pointed and often in branched extremities. 

 The muscles are either inserted into the integument directly or through the 

 medium of apod ernes, a clear transparent tendinous structure intervening^ 

 which appears to be continuous with the myolemma. The whole muscular 

 tissue is firm, but pale. 



The gland cells of the salivary tubes are 1-1 000th of an inch in 

 diameter ; those of the rectal papillae are l-500th of an inch in diameter ; 

 the conical epithelium of the stomach has a long diameter of 1 -1500th 

 of an inch. The liver cells are polygonal, filled with pigment and oil 

 globules, with a diameter of about l-1500th of an inch : all have well 

 marked nuclei. Adipo?e tissue does not exist, but large quantities of fat 

 are laid up in the folliculate glands and liver cells, especially in the former. 



Nerve cells vary from l-5000th to l-2500th of an inch in diameter ; 

 t hey are irregular in form, often being branched. The nerve fibres vary 

 very much in size ; those of the muscles branch, and end in loops ; others, 



