132 f&& HUMAfr EOD?. 



has a true secreting chamber at its end we get a compound 

 gland, tubular (6r) or racemose (F, H) as the case maybe. 

 In many cases the chief duct, in which the smaller ducts 

 unite, is of considerable length, so that the secretion is 

 poured out at some distance from the main mass of the 

 gland. 



A fully formed gland, ZT, is thus a complex structure, 

 consisting primarily of a duct, c, ductules, dd, and secret- 

 ing recesses, ee. The ducts and ductules are lined with 

 cells which are merely protective, and differ in character 

 from the secreting cells which line the deepest parts. The 

 cells lining the ultimate recesses differ in different glands, 

 and produce different liquids; consequently, though all 

 glands are built on much the same plan, they make very 

 varied secretions, the nature of the secretion of any gland 

 depending on the properties of its cells. 



The Complexity of the Alimentary Canal. We may 

 now return to our immediate subject, the alimentary canal. 

 This is not a simple tube, but presents several dilatations on 

 its course; nor is it a comparatively straight tube, as dia- 

 grammatically represented in Fig. 1, but, being much longer 

 than the regions of the body which it traverses, much of it 

 is packed away by being coiled up in the abdominal cavity. 



Subdivisions of the Alimentary Canal. The mouth- 

 opening leads into a chamber containing the teeth and 

 tongue, and named the mouth-chamber or bttccal cavity. 

 This primary dilatation is separated by a constriction (the 



A compound? How does it happen that the secretion is some- 

 times poured out at a distance from the main mass of the gland? 



Describe a fully developed gland. How is it that glands make 

 such different secretions? On what does the nature of the secretion 

 of a gland depend? 



How does the alimentary canal differ from a simple uniform tube? 

 Why is a great part of it coiled? 



Into what does the opening between the lips lead? 



