572 SUMMARY OF CURRENT RESEARCHES RELATING TO 



inward of mesenchymal wall forms paired valves at the orifices between 

 the ventral trunk and the caudal heart. The endothelium arises from 

 the flattening of some of the border-cells of the larger mesenchymal 

 cavities ; the connective-tissue endocardium comes from a concentration 

 and differentiation of the mesenchyme about the endothelial lining. 

 There is no true myocardium in the caudal heart, but a functional 

 myocardium arises from myoblasts in the mesenchyme. 



b. Histolog-y. 



Extra-cellular Protoplasm.*— F. K. Studnicka discusses a number 

 of cases to which this term is applicable. He instances the numerous 

 cell-bridges (cytodesms), which are now known, the mesogloea or meso- 

 stroma in Coelenterates, the matrical substance in various tissues, the 

 vitreous humour, the stream of extra- cellular protoplasm in Reissner's 

 fibre, outgrowths of cells such as pseudopodia and cilia and stalks, the 

 neurochord of some Invertebrates, and many other cases. Just as with 

 intra-cellular protoplasm, so with extra-cellular protoplasm there is great 

 variety — from gelatinous matrix to neuropilema. 



Minute Structure of the Endometrium of some Mammals.f — 

 (}. Lo Oascio finds that the uterine epithelium in a state of absolute rest 

 contains some quantity of lipoid substances. These are found partly 

 in the investing epithelium of the mucosa and partly in the glandular 

 tubes. The substances are elaborated by the plasma and destined 

 to be expelled into the uterine cavity and lumen of the glands. 

 The secretion is merocrinal, not holocrinal. Both in the investing 

 epithelium and in the glandular epithelium, the cells show a mitochon- 

 drial apparatus, but the investigator has not determined whether this 

 takes an active part in the process of secretion. 



Deposition of Pigment in Endothelium of Capillaries in Osseous 

 medulla. J — Hans Brass has studied this in rabbit, dog, rat, and cat. 

 The endothelial cells have a phagocytic capacity, taking in minute solid 

 particles, but no bacteria. In contrast to most vascular endothelium 

 cells, they take up dissolved carmin injected into the blood and deposit 

 it in granular form. In rabbits they contain a yellowish-brown pigment, 

 derived from haemoglobin, which is set free by the destruction of red 

 blood corpuscles. It passes to the endothelial cells in dissolved form 

 and gives no iron reaction. Thus, besides a slight phagocytic capacity, 

 the cells have a marked synthetic capacity, absorbing dissolved material 

 from the blood and depositing it in granular form. In the dog there is 

 phagocytosis, and the pigment arises from erythrocytes taken into the 

 endothelial cells. The pigment absorbed by the endothelial cells in the 

 case of the rabbit is apparently returned to the blood-forming elements 

 of the osseous medulla, and is doubtless used in the new-formation of 

 erythrocytes. 



* Anat. Anzeig., xliv. (1913) pp. 561-93. 



t Anat. Anzeig., xliv. (1913) pp. 197-202 (6 figs.). 



t Arch. Mikr. Anat., Ixxxii. (1913) Abt. 1, pp. 61-78 (1 pi.). 



