EXPLANATION OF THE PLATES. XV 



of attraction in each, select and remove from the capillary 

 vessels the matter necessary for the formation of the cells of 

 the internal layer. These after solution pass in succession 

 into the cavity of the cyst, to serve as nutriment for the 

 contained cellular mass. 



This mass is evidently the principal element of the 

 morbid growth. The cyst is a subsidiary or accessory part, 

 arranged for the protection and due supply of nourishment 

 for its principal. The cells of which this mass consists have 

 each its own nucleus or germinal centre. These 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 mother-cells, and those which 

 act as reproductive individuals for the whole morbid growth. 

 These latter cells are marked 6 6 in Figs. 2 and 3, and con- 

 tain numerous nutritive centres or germinal spots in their 

 interior. The flat cells of the white external layer appear to 

 be those individuals of the first class, which are about to 

 close their existence, their nuclei having disappeared ; their 

 food, therefore, no longer supplied to them, and their position 

 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 

 reproducers, the remaining parts performing the functions of 

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

 munities of animals certain individuals are set aside to re- 

 produce 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 portion of the human kidney. The 

 germinal spots of the gland are seen imbedded 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 Mr. Bowman. In other instances, as when the epithelia 

 are but slightly developed, it becomes difficult to decide 

 whether we have merely the germinal membrane, or both 

 the membrane and its epithelia before us. 



INTESTINAL VILLL PLATE IV. page 389. 



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

 has commenced. It has cast off its protective epithelium, 

 and displays, when compressed, a network of peripheral 

 lacteals. The granular germs of the absorbing vesicles, as 

 yet undeveloped, are seen under its primary membrane. 



