86 B. F. KINGSBURY 



As to the quite distinct question — whether the interstitial cells 

 of the testis, as such, form specific chemical substances which 

 determine the development of the secondary sexual characters, 

 or the appearance of sexual instincts — I only venture to suggest 

 that since there is no direct evidence of their being such specific 

 producers of 'hormones' of internal secretion, and since they 

 never occur separately as far as known to me from the indifferent 

 cells of the seminal tubules, considerable reluctance should be 

 felt in deciding that they alone are the 'gland' that produces 

 the substances with which the influence of the testis in the 

 organism is correlated. 



To Prof. S. H. Gage, the writer is indebted for numerous sug- 

 gestions which are here gratefully acknowledged. 



SUMMARY 



1. The interstitial cells are modified stroma cells, and hence 

 of connective tissue origin. 



2. Their origin in the adult as an hypertrophy of theca cells 

 during atresia folliculi is fully confirmed. 



3. In the fetus, new born and immature kitten, they appear 

 associated with the irregular so-called medullary cords and fol- 

 licle formations of these periods. 



4. Free lipoid granules appear in the indifferent cells of the 

 atretic follicles, medullary cords and irregular medullary follicles 

 in parts not associated with the ova. 



5. The development of interstitial cells appears to be corre- 

 lated with the activity of the indifferent or follicle cells in the 

 absence of germ cells. The suggestion is strong that an element 

 of degeneration is involved. 



6. The zone in which they occur conforms to the centrifugal 

 march of differential growth in the ovary. 



7. No morphological value is believed to attach to the dis- 

 tinction of a fetal (or presexual) from an adult grouping of the 

 cells. 



8. No evidence is found for regarding the interstitial cells as 

 constituting morphologically an intra-ovarian gland. 



