THE ALIMENTARY CANAL. 61 



gland-sac and its duct. This, according to Kowalevski, is 

 destined to develop the corresponding gland in the nymph. 



The salivary glands of insects have attained a classical 

 interest, owing to the various researches which have been 

 made on the nerve terminals and their relation to the secreting 

 epithelium. In the fly larva their nerves are derived from the 

 proventricular ganglion, which gives off numerous short nerves, 

 ending in the salivary cells. It appears to me that these are 

 processes of the ganglion directly continuous with the proto- 

 plasm of the secreting cells, and that only a few of the cells 

 those adjacent to the ganglion receive any. 



Weismann described a very remarkable structure, which he 

 calls a cell chaplet, connected with the external coat of the t\vo 

 salivary glands. He says : 



' It consists of a string of large cells closely united, which 

 hangs like a garland free in the body cavity. Its two 

 ends are connected with the salivary glands, and with a 

 muscular band from the dorsal vessel. It forms an arch, with 

 its convexity directed backwards, in the horizontal plane near 

 the back. This string of cells has no duct/ [2, p. 132.] 



The Malpighian Vessels are two in number, but each divides 

 into two tubules about two mm. from its junction with 

 the intestine. I cannot give the length of these tubules ac- 

 curately, as they are not easily unravelled, but it is considerably 

 more than a centimetre. They are at once recognised by their 

 dark brown colour, and they become intensely black when 

 treated with osmic acid. 



The Malpighian tubes have no muscular coat ; but consist 

 of a structureless external cuticle, lined with a single layer of 

 cells, two, or at most three, cells entirely surrounding the tube 

 (PI. I., Fig. 8). 



Externally they exhibit a moniliform appearance, the large 

 cells projecting as hemispherical protuberances on the surface. 

 The lumen of the gland is small and irregularly flattened. 

 The cells measure 70" to 80", and have large, nearly spherical 

 nuclei. 



The cell protoplasm is distinctly reticular, and contains 



