316 



EPITHELIAL AND ENDOTHELIAL TISSUE. 



the endothelia which directly cover the capillary blood-vessels 

 being decidedly larger than those covering the delicate intersti- 

 tial fibrous connective tissue. After staining with silver, solid 

 dark brown, circular spots appear in the brown basis-substance, 

 and are far more numerous in the endothelia between, than in 

 those above blood-vessels; or there are simple ring-like forma- 

 tions, or light openings, surrounded by a wreath of small endo- 

 thelia. The openings at the angles of the polyhedral bodies are 

 termed stomata j those in the middle of a brown line of cement- 

 substance, stigmata, both being essentially identical viz.: open- 

 ings of the lymphatics. Similar formations were found also in the 

 endothelial layer of capillary 

 lymph- and blood-vessels, and 

 J. Arnold drew attention to 

 their largely increased num- 

 ber in the blood-vessels of 

 inflamed tissues, indicating 

 an active emigration of color- 

 less blood-corpuscles. 



In thin specimens of sil- 

 ver-stained endothelia the 

 dark brown cement-sub- 

 stance is never smooth, but 

 more or less fluted, and at 

 regular intervals traversed 

 by delicate light lines, which 

 unquestionably correspond 

 with the "thorns" or fila- 

 ments not affected by the 

 silver salt. (See Fig. 134.) 



The crystalline lens is 



FIG. 134. ENDOTHELIAL 

 OF THE 'PERITONEUM 

 STAINED WITH NITRATE OF SILVER. 



N, nuclei faintly visible in the endothelia ; C, 

 dark brown, interrupted lines of cement-sub- 

 stance ; SO, stomata at the angles ; SI, stigmata 

 in the middle of the brown lines. Magnified 600 

 diameters. 



INVESTMENT 



OF A PUP, 



known to be a formation of 

 the horny germ-layer, the 

 epiblast; it is, therefore, an 

 epithelial structure, com- 

 posed of flat ribbons, which 

 are arranged in a peculiarly radiating and concentric manner. 

 The peripheral ribbons are possessed of oblong nuclei. Delicate 

 fringes have been noticed along the edges of torn ribbons of the 

 lens, but their significance was not understood. They are the 

 same formations as exist in all epithelia viz., Max Schultze's 

 " thorns," the connecting filaments of the ribbons. The reticular 



