Age Factor in Some Prenatal Endocrine Events 21 



Briefly, it was noticed (Jost, 1951) that in the foetuses 

 which were decapitated before the initiation of somatic 

 sexual differentiation, testicular activity remained weak: on 

 day twenty-eight the prostate was as reduced as in foetuses 

 castrated on day twenty-one, and likewise the external geni- 

 talia were feminine. 



The importance of the age factor in hypophyseal function 

 was studied in two series of foetuses ; some were decapitated 

 early and killed at one-day intervals thereafter, others were 

 decapitated at one-day intervals and killed at the same final 

 stage (day twenty-eight). The analysis of the results indicates 

 that the testis has some activity even in the absence of the 

 pituitary gland. It works in a normal manner until approxi- 

 mately day twenty-two as judged from the first steps of differ- 

 entiation of the genital tract; afterwards, mainly between 

 day twenty-two to twenty-four, the pituitary gland is needed 

 for normal testicular function; after day twenty-four it can 

 be removed without suppressing masculine organogenesis. 



Relationship between hypophysis and thyroid also indi- 

 cated that, until the twenty-first or twenty-second day, the 

 thyroid differentiation and specialization proceeds normally 

 in the headless foetuses; afterwards the pituitary gland be- 

 comes necessary (Jost, 1953a, 19536). 



On the adult animal, the McManus technique (periodic 

 acid - Schiff ) has been shown to give indications about those 

 pituitary cells which produce gonadotrophic or thyrotrophic 

 hormone. Therefore this procedure was applied to the hypo- 

 physis of the rabbit foetus (Jost and Gonse, 1953). McManus- 

 positive material accumulates in an increasing number of 

 pituitary cells from day nineteen until day twenty-two to 

 twenty-three and then diminishes in a significant manner; 

 this last point will be illustrated here only by one case con- 

 cerning litter mates, two of which were studied on day 

 twenty-three and two others on day twenty-eight. The average 

 numbers per section of distinctly stained cells, counted in 

 three medial sagittal sections, distant 125jjl, were respectively 

 232 and 263 on day twenty-three in comparison with 65 and 77 



