GLANDULAR STRUCTURES. 725 



may be accomplished with the utmost facility, is well adapted to 

 give an idea of the essential nature of glandular structure. Among 

 Yertebrated animals, the Salivary glands, the Pancreas (sweet- 

 bread), and the Mammary glands, are well adapted to display the 

 follicular structure (Fig. 38b) ; nothing more being necessary than 

 to make sections of these organs, 

 thin enough to be viewed as p IG ggg 



transparent objects. The Liver 

 of Vertebrata, however, presents 

 certain peculiarities of structure, 

 which are not yet fully under- 

 stood ; for although it is essen- 

 tially composed, like other Glands, 

 of secreting cells, yet it has not yet 

 been determined beyond doubt 

 whether these cells are contained 

 within any kind of membranous 

 investment. _ The Kidneys of Ver- urinate Follicles of Mammary 

 tebrated animals are made-up ot Gland, with their Secreting Cells 

 elongated tubes, which are straight a, a, containing nuclei b, b. 

 and are lined with a pavement 



epithelium in the inner or 'medullary' portion of the kidney, 

 whilst they are convoluted and filled with a spheroidal epithelium 

 in the outer or ' cortical.' Certain flask-shaped dilatations of 

 these tubes include curious little knots of blood-vessels, which are 

 known as the 'Malpighian bodies' of the kidney; these are well 

 displayed in injected preparations. — For such a full and complete 

 investigation of the structure of these organs as the Anatomist 

 and Physiologist require, various methods must be put in practice 

 which this is not the place to detail. It is perfectly easy to de- 

 monstrate the cellular nature of the surface of the Liver, by simply 

 scraping a portion of its cut surface ; since a number of its cells 

 will be then detached. The general arrangement of the Cells in 

 the lobules may be displayed by means of sections thin enough to 

 be transparent ; whilst the arrangement of the Blood-vessels can 

 only be shown by means of Injections (§ 577). Fragments of the 

 tubules of the Kidney, sometimes having the Malpighian capsules 

 in connection with them, may also be detached by scraping its 

 cut surface ; but the true relations of these parts can only be shown 

 by thin transparent sections, and by Injections of the Blood-vessels 

 and tubuli. The simple follicles contained in the walls of the 

 Stomach are brought into view by vertical sections ; but they 

 may be still better examined by leaving small portions of the 

 lining membrane for a few days in dilute nitric acid (one part 

 to four of water), whereby the Fibrous tissue will be so softened, 

 that the clusters of Glandular Epithelium lining the follicles (which 

 are but very little altered) will be readily separated. 



567. Muscular Tissue. — Although we are accustomed to speak 



