266 



ORIGIN OF THE GLANDS. 



the mucous lamina of the germinal membrane, and, like the 



salivary glands, the lungs, 

 the liver, the pancreas, 

 are to be regarded as 

 evolutions of this mem- 

 brane, or of the intesti- 

 nal canal. This view is 

 liable to misapprehen- 

 sion, by the process of 

 ^ evolution being conceiv- 



ed in a purely mechani- 

 cal way. The general 

 plan of the evolution of 

 the secreting glands is 

 as follows. At the place 

 where the gland is to be 

 formed take the liver 

 or the pancreas as a par- 

 ticular instance (figs. 269, 

 270,and271,a,6),arough 

 projection appears upon the intestine. This projection consists 



of a delicate, finely granular, 

 and pale tissue the blastema, as 

 it is called, which was in former 

 times looked upon as without 

 structure. By watching this part 

 we see how particular divisions 

 make their appearance within it 

 (fig. 272), which by and by form 

 lobules or club-shaped bodies, 

 and are the elements or ground- 

 work of the future csecal canals, 

 where these are to appear. It 

 is now that a kind of solution of 

 the internal contents of the mass 

 or masses takes place, or rather 

 that distinct walls with double 



contours are produced. This is to be seen most beautifully 

 displayed in the lungs (fig. 273).* And now appears the 



Fig. 271. The same parts in another 

 emhryo more highly magnified, to exhibit 

 the undoubtedly cellular and racemose 

 structure of the liver and pancreas. The 

 references are likewise the same. 



Fig. 272. The liver more ad- 

 vanced than in the last figure from 

 an embryo of the fowl of the sixth 

 day. It is not only divided into 

 two lobes, but shows minute cceca 

 in its interior. After Muller. 



* The lungs are to be viewed as the prototype of all secreting glands. 



