606 VETERINARY PHYSIOLOGY 



become arranged in tubules, forming {a) the spermatogonia, 

 from which the spermatozoa are produced (p. 620), and (6) 

 certain larger cells, the supporting cells of Sertoli, (c) Some 

 of the mesothelial cells remain outside and between the tubules, 

 and form the interstitial cells of Ley dig. These are large cells, 

 and they contain a large amount of lipoids. Some observers 

 maintain that they are really connective tissue cells. 



B. Ovaries. — In the ovaries the ingrowing mesothelial cells 

 form separate masses, the Graafian follicles, (a) One of the 

 cells enlarges and becomes the ovum, the female gamete (p. 619) ; 

 while (6) the others remain smaller and form the cells of the 

 zona granulosa, (c) In many animals between the Graafian 

 follicles a considerable number of the mesothelial cells remain 

 as the interstitial cells of the ovary. 



The interstitial cells of the testis and ovary I'esemble one 

 another very closely and are both very similar to the cells of 

 the inter-renal organ which forms the cortex suprarenalis. 

 They are very rich in lipoids and especially in cholesterol 

 compounds. 



2. Physiology- — The part played by the gonads in the process 

 of reproduction will be considered later (p. 618). At present 

 their action as endocrinetes has to be dealt with. 



A. Testes. 



(1) Removal- — Removal of the testes in young boys and in 

 young animals leads to a persistence of the infantile type of body, 

 and to the absence of development of the secondary sexual 

 structures, such as the prostate gland, the hair of the body and 

 face in men, the horns of sheep and cattle, and the antlers of deer. 



The temperament is generally phlegmatic, and hence a 

 gelded horse is more easily managed. Castrated animals fatten 

 more readily. The cartilaginous growth of bone tends to persist, 

 and hence the bones tend to be longer and more slender than 

 in the entire animal. 



(2) Precocious Development- — In man this is accompanied 

 by premature development of the secondary sexual organs, by 

 abnormal growth of hair, premature union of the epiphyses of 

 the long bones, and increased growth of the bones in thickness. 

 These conditions have been observed in connection with tumour 



