DEVELOPMENT OF CARTILAGE. 99 



once the birthplace of young leucocytes, and the grave of such 

 red corpuscles as are growing old. 



§ 78. So much for the genesis of the conjoint blood-vascular 

 and connective-tissue system. AYe mark the distinction be- 

 tween its stationary and its mobile cells. To the former class 

 belong what used to be called connective-tissue corpuscles, 

 the endothelia of the blood-vessels and lymphatics, the stellate 

 and anastomosing cells of the lymph-sinus and the splenic pulp, 

 and finally the epithelia which line the serous cavities, since 

 these are (according to Reclclingliauseri) in direct communication 

 with the lymphatic sj^stem. The mobile cells are represented by 

 the blood-corpuscles, and of these the colourless ones are pecu- 

 liarly prone to accompany the nutrient fluid in its passage 

 through the walls of the minuter vessels ; after traversing which, 

 some, as" migratory corpuscles of the connective tissue," place 

 themselves at the disposal of the growing organs to be employed 

 in the constructive process, while others make their way back 

 into the blood through the lymphatics. The stationary cor- 

 puscles originate from the mobile cells ; how the latter originate 

 is still unknown. The cells in the parenchyma of the lymphatic 

 glands and the spleen have the best claim to be regarded as their 

 normal source. Yet if we bear in mind how the lymphatic 

 glands themselves originate, we shall probably have to admit, 

 as a fundamental postulate, that all colourless corpuscles, when 

 once they have escaped from the circulating current, begin 

 to migrate and to undergo division. 



§ 79. Passing on to consider the growth of the remaining 

 organs of the body, we will devote our first attention to Cartilage 

 and Bone. Everybody knows that in sections of young cartilage 

 the cells are (wdtli hardly an exception) distributed through the 

 matrix in groups, or at all events in pairs. The connexion of 

 any two cells is evident from their each having a convex and a 

 plane surface, the j^lane surfaces being opposed to one another. 

 One is involuntarily led to think that they form the two halves 

 of a globular body. That the appearances are really due to 

 fission is shown from the occurrence of pairs of cells, which are 

 still contained in a common capsule. Add to this visible pro- 

 liferation of the cells, the intercalation of fresh intercellular sub- 

 stance which separates the independent halves of the divided 

 cell to the proper extent, and we have the well-known scheme, 



