TISSUES OF THE BODY. 



349 



which they are, without exception, destroyed, or the cavity remains 

 closed during the whole of life, the contents exuding through the 

 parietes. To the first of these species the glandular elements of the 

 ovaries belong; to the second, those of the thyroid body. In man, 

 however, we never meet with a whole gland formed of one closed capsule 

 by itself, as is the case with the tubular follicles. The few organs in our 

 body which may be numbered with the last species, are composed of a 

 multitude of elements of this kind imbedded in a connective-tissue ground- 

 work. 



REMARKS. The word "acinus " is also made use of to designate the gland-vesicle, 

 so that it is as well, perhaps, to avoid the term entirely. 



195. 



The second, and more important elementary structures of the organs 

 with which we are now engaged, are the gland cells. These are derived 

 from the corneous and intestinal glandular embryonic leaves, and in 

 keeping with their origin, never completely lose their epithelial characters. 



In the bodies of many of the lower animals the significance of these 

 gland cells appears in the most striking way. The interesting discovery, 

 namely, has been made, that in them there exist glandular organs which 

 consist of but one single cell only. 



Within the cavities of glandular organs these cells are either packed 

 closely together without order, filling out the former, or they clothe their 

 internal surfaces like epithelium. Not ^infrequently, when so arranged, 

 their -figure is polyhedral. They may also occur either arranged in one 

 single layer, or forming a double lamina. 



At the outlets of glands these cells are continuous with those of the 

 neighbouring epithelial formations, and frequently without any sharp line 

 of demarcation, so that the latter may be looked upon as having become 

 gradually transformed into glandular elements. Indeed, wo meet with 



Fig. 336. Cells from the peptic glands of 

 man. a, cell without a membrane; 

 6, a nucleus enveloped in a residue of 

 the body of the cell ; c, a cell with two 

 nuclei; d-g, cells with sharper contour 

 and decrease in the number of granules 

 usually contained in such. 



Fig. 337. Human hepa- 

 tic cells, a, one with 

 a single nucleus; ft, 

 another with two of 

 the latter. 



many glandular organs whose cells are but little different, at least anato- 

 mically, from those of the epithelia. 



The different species of cells which are met with in the latter have their 



