KXl'LAXATION OF THE PLATES. XV 



«»f attmctiijii in each, select aud remove from the caiiilhirv 

 vessels the matter necessary for the formation of the cells of 

 the internal layer. These alter solution pass in succession 

 into the e^ivity of the cyst, to seiTe as nutriment fur the 

 contained cellular mass. 



This mass is evidently the principal element of the 

 morbid growth. The cyst is a subsidiary or accessor^' i)art, 

 arranged for the j)rotection and due sujiply of nourishment 

 for its jirincipal. The cells of which this mstss consists have 

 each its own nucleus or genniual centre. Tliese cells would 

 appear to be of two classes — those whose nuclei produce 

 young cells in their interior for their own nutrition, but not 

 for the reproduction of new muther-cells, aud those which 

 act as reproductive individuals for the whole morbid growth. 

 These latter cells are marked h b in Figs. 2 and .3, and con- 

 tain numerous nutritive centres or gerndnal spots in their 

 interior. The Hat cells of the white external layer api>ear to 

 be those individuals of tlie fii-st clas.-<, Mhich are about to 

 clo.se their existence, theu* nuclei having disapj)eared ; their 

 food, therefore, no longer supi>lied to them, and their jM^sitiou 

 in the mass removed to the exterior by the eccentric 

 development of the younger and more active neighbouring 

 cells. In a morbid mass of this kind, as in the textures and 

 organs of an animal generally, certain parts are set aside as 

 reproducei's, the remainijig parts perfonuing the functions of 

 the whole mass, texture, or organ ; just as in cei-tain com- 

 munities of animals certain individuals arc ."set a-side to re- 

 2)roduce the swarm, the others are devoted to the duties of 

 the hive. 

 Fig. 4. Two portions of the primary or germinal membrane from the 

 tubes of the tubular porti(jn of the human kidney. The 

 germinal spots of the gland are seen indn-dded in the sub- 

 stance of the membrane. The external layer of this mem- 

 brane, which may occasionally be seen with the nuclei 

 detached from it, is the basement or homogeneous membrane 

 of ^Ir. Bowman. In other instances, as when the epithelia 

 are but slightly developed, it becomes difBcult to decide 

 whether we have merely the germinal membrane, or both 

 the membrane and its epithelia before us. 



INTESTINAL VILLI.— Plate IV. j-age 389. 



Fig. 5. Extremity of a villus immediately before absorjUion of chyle 

 has connnenced. It has cast olf it-s protective epithelium, 

 and displays, when compre.<5sed, a network of jieriphenil 

 lacteals. Tlie granular gt-rms of the absorbing vesicles, iU< 

 yet undeveloped, are seen under its primaiy mend»raue. 



