54 



HYPOPHYSIS->OVARY -> OVIPOSITOR. 



II 



X 



exogenous and still present stimulus to cause a second extrus- 

 ion. The hypophysis curve, therefore, falls again, represent- 

 ing the /j-phase. 



In this process the lower limit of the hypophysis curve 

 occurs after the upper limit of the a-curve, for it is not the 

 extrusion phase itself but the restitution phase following it 

 which is plotted. Thus, the time of the restitution phase of 

 the hypophysis and that of corpus luteum formation partly 

 coincide, so that the maximum of the hypophysis curve cor- 

 responds to the minimum of the a-curve (progesterone, 

 androsterone). This phenomenon points to the correlation 

 between the hypophysis and the ovary. 



The rather striking agreement between the maxima sug- 

 gests a quantitative correlation between the processes. Since 

 the ovary, as the secondary system in this chain-reaction, 

 produces a sufficient number of ova for the formation of 

 corpora lutea, one is justified in saying that a small amount 

 of luteinising hormone produces only a small number of 

 corpora lutea; in other words, the ovary reacts quantitatively 

 to the pituitary hormone. 



It is plain, therefore, that response in the bitterling pre- 

 sents the following picture (Fig. 49 ) : the exogenous stimulus 

 (steroid hormone) enters the blood through the gills and 

 affects the hypothalamus. The latter then acts, possibly 

 through nervous channels, on the hypophysis, which, by 

 means of the luteinising hormone stimulates the ovary, to 



hypothalamus 



corpus luieum 

 oviduct in 



Fig. 49. Diagram showing the concatenation: stimulating agent-^ 

 hypophysis .^ ovary "^ovipositor. 



