THE SALIVAEY GLAND, 79 



same parts as in the previous stage. These were, it will be 

 remembered, (1) what I may call a vesicular internal part, ex- 

 tending to the hind end of the appendage and forwards as an 

 anterior diverticulum, and opening into (2) a tubular part, 

 projecting ventrally and opening to the exterior. 



In Stage r the vesicular internal part (Plate VIII, figs. 36, 

 37, I. s, V. 3) has not only lost its connection with the dorsal 

 (median) part of the somite, but its peripheral part — viz. that in 

 the appendage — has become largely obliterated by the increase in 

 the thickness of its mesodermal walls, and by the growth of the 

 slime-gland rudiment. At the same time the tubular part has 

 become longer and more twisted (figs. 37, 38, 1. st.S), and its 

 external opening covered up by the lips, which have met on the 

 ventral surface (Plate II, fig. 36). The tubular part, therefore, 

 no longer opens freely, but into the posterior part of the buccal 

 chamber. 



I will now describe more in detail the structure of the two 

 parts during Stage F. 



The inner walls of the internal vesicle retain (Plate VIII, 

 figs. 36, 37) the character presented by the walls of the 

 anterior diverticulum of the previous stage (a. v. Plate VII, 

 fig. 23 b) ; i. e. the nuclei are relatively far apart, and separated 

 by a slightly staining protoplasm. The outer wall, on the 

 other hand, is reduced to a thin layer. 



The tubular portion I shall now call the nephridium. Its 

 opening into the vesicle, shown in fig. 38, is a well-defined 

 structure, which I shall call the funnel of the nephridium. 

 The external opening of the nephridium (fig. 37) is anterior to 

 the funnel. The course of the tube at this stage will be under- 

 stood by an inspection of figs. 37, 38, 38 a. It will be observed 

 from these that the nephridium — the part marked I. s. t. 3 in 

 fig. 38 — projects back as a tube (fig. 38 a, I. s. t. 3 = sal. gl.) 

 which ends blindly. This backwardly projecting part gains an 

 enormous extension in the later stages, and is known in the 

 adult as the salivary gland. 



Kennel, who has correctly recognised the nephridial na- 

 ture of the salivary gland, has made what I cannot but 



