40 HOMER WKEELON 



The interstitial cells, according tp Bouin and Ancel, Chapin, Allen, 

 and Whitehead, appear in the primitive genital tra,ct and become func- 

 tional before the spermatic cells are fully differentiated. Whitehead has 

 shown clearly that the intertubular tissue of the testis of the pig embryo 

 in stages immediately preceding the appearance of interstitial cells is a 

 mesenchymal structure derived from the mesothelium of the genital ridge. 

 Histologically, this tissue is a connective tissue syncytium consisting of 

 cells and an exoplastic network of fibrils. The cells are scarcely more 

 than naked nuclei, though some have a small collection of cytoplasm at 

 one pole. From the cells of this tissue interstitial cells are developed by 

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

 branches are connected with the general exoplastic network, so that the 

 cells retain the syncytial arrangement of their ancestors. They increase 

 rapidly in number and size and soon lose their branches. 



In the pig the interstitial cells pass through two phases of growth 

 with a phase of atrophy intervening. Growth is very rapid from their 

 appearance 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 stage of naked nuclei. This process 

 reaches its acme in the embryo 14 cm. long and synchronous with it there 

 is an extensive growth of the seminal tubules, so that they are greatly 

 convoluted and the intertubular spaces correspondingly narrowed. In the 

 embryo 20 cm. long the interstitial cells enter upon their second phase of 

 growth which attains its maximum in the pig 28 cm. long, or very near 

 to term. At this time the cells are enormously increased and constitute 

 the predominating feature of the microscopic picture. 



In the adult the interstitial cells appear as rounded or polygonal 

 elements which vary greatly in different species and from time to time 

 in the same individual (Hofmeister). The nucleus usually lies eccen- 

 trically and is surrounded by a condensed endoplasm which merges into a 

 less dense, vacuolated ectoplasm. Soluble and insoluble pigments are 

 present (Regaud, von Ebner, Mott, Duesberg and Whitehead). Lipoid, 

 although variable in amount, is never entirely absent from these cells 

 and may appear in the form of phosphatid lipoid material, cholesterin 

 esters, or neutral fat (Hanes and Rosenbloom, Whitehead, and Ras- 

 mussen). 



In man, according to Ishibashi, the interstitial cells are of variable 

 structure according to age. They are conspicuously numerous in children, 

 and at certain stages closely resemble fibroblasts. Mott observed 100 

 autopsy cases from birth to 86 years, and found that the interstitial cells 

 appeared in great numbers at birth and contained lipochrome material. 

 At puberty the tubules are closely approximated and the interstitial lipoid 

 is abundant. Cases dying before puberty (of chronic diseases) demon- 

 strate an arrest of granules in the interstitial cells. 



