116 GENERAL ANATOMY OF THE TISSUES. 



The formation of certain secretions {^TJric acid and hilin in Mollusks, 

 hilin in Crustacea] within special spontaneously enlarging " secreting 

 vesicles," (Nageli, H. Meckel), which may be compared to the yelk 

 vesicles (§ 6). 4. The colossal size (up to 0*1 of a line) of many glan- 

 dular cells of Insects, and the peculiar ramifications of their nuclei. 



Literature. — J. Muller, " De Glandularum secernentium structura, 

 penitiori," Lips. 1830; H. Meckel, " Micrographie einiger Driisenappa- 

 rate niederer Thiere," in Miill. "Arch.," 1846 ; Fr. Leydig's " Verglei- 

 chend-anatomische Abhandlungen," in "Zeitschrift fiir wiss. Zool." 



§ 30. Tissue of tlte Blood-vascular Cflands. — Under this denomination 

 are most appropriately comprised, a series of organs, which agree in this, 

 that in a peculiar glandular structure, they elaborate from the blood or 

 other juices certain substances which arc not excreted by special, per- 

 manent, or periodically-formed excretory ducts, but simply by infiltra- 

 tion from the tissue, and are afterwards applied in one way or another 

 to the general purposes of the organism. 



It may be, that this wide definition includes organs, which it will be 

 necessary to separate in future ; but with our present slight knowledge 

 of these structures, it is the only one which is possible without entering 

 more fully into the subject. 



The essential glandular tissue of the organs in question appears under 

 the following forms : — 



1. As a parenchyma of larger and smaller cells, imbedded in a stroma 

 of connective tissue. Supra-renal bodies, anterior lobes of the hypo- 

 physis cerebri. Some of the cells here attain the great size of 0*04 of 

 a line; and then contain, together with a granular substance, many 

 nuclei, and perhaps secondary cells. 



2. As closed follicles, each of which consists of a memhrana propria 

 with an epithelium upon its inner side, and has clear contents: thyroidea. 

 The follicles, which are not enlarged cells, are surrounded by a large 

 quantity of connective tissue, and are united by it into smaller and 

 larger lobules. 



3. As closed follicles, with a membrane of connective tissue, and con- 

 tents consisting of nuclei, cells and some fluid. Among these I enume- 

 rate — 



a. The solitary follicles of the stomach and intestine ; and 

 h. The aggregated follicles of the small intestine, or Peyer's patches 

 (in animals those of the stomach and large intestine also), both of which 

 contain numerous bloodvessels in the interior of the follicles. 



c. The follicular glands in the root of the tongue, the tonsils, and 

 the pharyngeal follicles, which in the walls of their sacs, contain many 



