116 JESSE LE ROY CONEL 



duct is continuous with that of the tubule. The tubules vary 

 in length, the shortest averaging 0.07 mm., the longest 0.2 mm. 

 \\Tien long, they are more constricted than when short, the out- 

 side diameter of the narrowest tubule measured being 0.04 mm. 

 The size of the opening where the tubules enter the duct varies, 

 but approximates 0.12 mm. in diameter. Figure 58 is a diagram- 

 matic reconstruction of a plain tubule. 



The compound tubule is strikingly different from the plain, as 

 is shown by figure 59, which is a reconstruction of a Malpighian 

 body with a tubule of this type. It consists of two parts, a 

 neck and a trunk. All of the Malpighian bodies of all the speci- 

 mens examined, except the one described above, have this type 

 of tubule. The neck is that part of the tubule which joins the 

 Bowman's capsule, and in structure and appearance it is exactly 

 like the plain tubules. It consists of short, columnar cells of 

 approximately equal height and which have very little cytoplasm. 

 The nuclei stain much more deeply than those of surrounding 

 tissues, so that the epithelium of the neck is easily distinguished 

 from that of the trunk. The cells of the neck gradually decrease 

 in height as they approach Bowman's capsule, and are continu- 

 ous with the cells of the single layer of squamous epithelium which 

 Hnes the capsule. The neck is variable in width and length 

 within narrow limits in different specimens and in different 

 tubules of the same specimen. An idea of the dimensions may be 

 had from one specimen : Outside diameter at entrance to trunk of 

 tubule, 0.35 mm., and at entrance to capsule, 0.078 mm.; length, 

 0.4 mm. The neck is sometimes as much as twice this length, 

 however. At the proximal end of the neck the epithelial cells 

 and basal membrane are continuous with the cells and basal 

 membrane, respectively, of the trunk of the tubule. The tran- 

 sition from the cells of the neck to those of the trunk is gradual, 

 as shown in figm'e 60. 



The trunk of the compound tubule is exactly like the mesoneph- 

 ric duct in structure. It consists of an epithelium of high colum- 

 nar cells which are arranged in ridges, and cells and ridges are 

 of approximately the same height as those of the duct. At the 

 anterior end of the duct this portion of the tubule is often as 

 large in diameter as the duct itself. Farther posteriorly, how- 



