TISSUES, ORGANS, AND SYSTEMS. 



103 



certain secretions [Uric acid and bilin in Mollusks, bilin in 

 Crustacea] within special spontaneously enlarging " secreting 

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

 vesicles (§ 6). 4. The colossal size (up to 0-T") of many glandular 

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



Literature. — J. Midler, ' De Glandularum secernentium 

 structura penitiori/ Lips. 1830 ; H. Meckel, ' Micrographie 

 einiger Drusenapparate niederer Thiere/ in Mull. ' Arch./ 1846 ; 

 Fr. Leydig's 'Vergleichend-anatomische Abhandlungen/ in 

 'Zeitschrift fiir wiss. Zool/ 



§ 30. 



Tissue of the Blood-vascular Glands. — Under this denomina- 

 tion are most appropriately comprised, a series of organs, which 

 agree in this, that in a peculiar glandular structure, they elabo- 

 rate from the blood or other juices certain substances which are 

 not excreted by special, permanent, or periodically-formed excre- 

 tory ducts, but simply by filtration from the tissue, and are 

 afterwards applied in one way or another to the general pur- 

 poses 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 enter- ^. . „ 



• {. . F'g- 43. 



ing more fully into the 

 subject. 



The essential glandu- 

 lar 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. Su- 

 prarenal bodies, anterior 

 lobes of the hypophysis 

 cerebri. Some of the cells 



Fig. 43. A few of the glandular vesicles from the thyroid gland of a child, x 250 : 

 a, connective tissue between them ; f/, membrane of the glandular vesicles; c, their 

 epithelium. 



