38 HISTOLOGY. 



b. Mesodermal, e. g., uterine glands. 



c. Entodermal, e. g., gastric and intestinal glands. 

 3. Compound glands. 



a. Ectodermal, e. g., mammary and lachrymal glands. 



b. Mesodermal, e. g., epididymis and kidney. 



c. Entodermal, e. g., pancreas and liver. 



II. Epithelial glands, with obliterated ducts, producing internal secretion. 



a. Ectodermal, pineal body; both lobes of the hypophysis. 



b. Entodermal, thyreoid gland. 



III. Epithelioid glands, never having duct or lumen, producing internal 

 secretions only. 



a. Ectodermal (through their relation to the sympathetic 



nerves), glomus caroticum; glomus coccygeum; and me- 

 dulla of the suprarenal gland. 



b. Mesodermal, cortex of suprarenal gland; interstitial cells of 



the testis; corpus luteum. 



c. Entodermal, islands of the pancreas; epithelioid bodies in 



relation with the thyreoid gland; thymus in its early stages. 



IV. Cytogenic glands, producing cells. 



a. Mesodermal, epithelial, the ovary and testis. 



b. Mesodermal, mesenchymal, the lymph glands, haemolymph 



glands, spleen, red bone marrow, and many smaller struc- 

 tures. 



, THE MESENCHYMAL TISSUES. 



In an early stage the embryo is composed of two tissues, epithelium 

 and mesenchyma. Mesenchyma has already been defined as a non-epithelial 

 portion of the mesoderm composed of branching cells. Their protoplasmic 

 processes anastomose, forming a continuous network of protoplasm, a 

 syncytium, in the meshes of which is a homogeneous intercellular substance 

 or matrix (Fig. 22, page 23). Those derivatives of mesenchyma which 

 diverge greatly from this embryonic type will be reserved for later considera- 

 tion. Such are the vascular systems, smooth muscle and certain epithelioid 

 cells. ReticuLar tissue, mucous tissue, connective tissue, tendon, cartilage 

 and bone, sometimes grouped as the supporting tissues, may now be con- 

 sidered in turn. They are all mesenchymal tissues which have undergone 

 transformations both of their cells and of the intercellular substance. 



RETICULAR TISSUE. 



Reticular tissue is that form of adult tissue which most closely re- 

 sembles mesenchyma. It is a network of cells with a fluid intercellular 



