R. H. Whitehead 181 



and once, in a pig of 3.5 cm., a small collection was seen in a Leydig's 

 cell just beneath the albnginea. They are not yolk granules, for they 

 do not stain with osmic acid, and no similar granules are seen in the 

 coelomic epithelium elsewhere. A probable explanation of their nature 

 is furnished by the changes which occur in the germinal epithelium at 

 this time. Its cells become vacuolated, and are soon reduced to the 

 squamous cells which cover the tunica vaginalis. So that the granules 

 found in the cells while these changes are going on are probably the 

 products of a hyaline degeneration of the cytoplasm. 



Summary. 



The intertubular tissvie of the testis of the pig embryo in stages imme- 

 diately preceding the appearance of Leydig's cells is a mesenchymal 

 structure derived from the mesothelium of the genital ridge. Histo- 

 logicalh', it is a connective-tissue syncytium, consisting of cells and an 

 exoplasmic network of fibrils. The cells are scarcely more than naked 

 nuclei, though some have a small collection of cytoplasm at one pole 

 (Fig. 1). . 



From the cells of this tissue Leydig's cells are developed by growth 

 of cytoplasm. At first they are markedly branched ; some of the branches 

 are connected with the general exoplasmic network, while others unite 

 with one another to form a network, so that the cells retain the syncytial 

 arrangement of their ancestors (Figs. 2 and 3). They increase in 

 number and size very rapidly, and soon lose their branches. At first 

 they may have various sizes and shapes, but one form soon predominates. 

 Such a typical Leydig^s cell is polygonal, its cytoplasm is very granular, 

 and its nucleus is eccentric and contains a large nucleolus. Mitotic 

 figures can be seen in all the earlier stages. 



Leydig's cells pass through two phases of growth, between which a 

 phase of atrophy intervenes. Growth is very rapid from their appear- 

 ance in the embryo 2.4 cm. long until the length of 3.5 cm. is reached. 

 This is followed by the phase of atrophy, during which the cells return 

 almost to their first state of nearly naked nuclei (Figs. 4 and 5). This 

 process reaches its acme in the embryo l-i cm. long. Synchronous with 

 it there is extensive growth of the seminal tubules, particularly in length, 

 so that they are much convoluted, and the intertubular spaces are cor- 

 respondingly narrowed (Fig. 6). In the embryo 20 cm. long the cells 

 enter upon the second phase of growth, which attains its maximum in 

 the pig of 28 cm., very near to term. Here the cells are enormously 

 increased in number and size, so that tljey constitute the predominating 



