THE REPRODUCTIVE ORGANS 



385 



The positions of the plotted points in Figs. 120 and 121 suggest that at least in the 

 case of Fin whales there is a general increase in the weight of the ovary from 20 m. 

 (at about which length sexual maturity is reached) up to 22 m., that a maximum is 

 reached here, and that there is subsequently some regression. This apparent regression 

 may be a coincidence or it may be an indication of actually different conditions in the 

 very large whales. The two whales of 23-6 and 24-15 m., plotted in Fig. 121, had 

 thirteen and twenty corpora lutea respectively, and the fact that in spite of this their 

 ovaries weighed so little, supports the suggestion that the ovaries do become lighter in 

 the largest whales. 



(b) Grozvt/i of the Ova 



It will be convenient next to trace the growth of the ovum and development of the 

 Graafian follicles. Sections of the ovary in young foetuses show large numbers of 

 deeply-staining nuclei towards the surface. In a 276 m. foetus the germinal nuclei 



e-!^— 



-■■-g-"- 





Fig. 122. Section through ovary of a 2-76 m. foetus 

 of a Fin whale. o.«., germinal nuclei ; p., Pfluger's 

 tubes. 



Fig. 123. Early Graafian follicles in 

 6-05 m. foetus of a Fin whale. 



were collected in cavities (Pfluger's tubes), the intervening tissue being connective 

 tissue and large blood spaces (Fig. 122). In a 6-05 m. foetus definite Graafian follicles 

 are present some distance in from the surface (Fig. 123), while near the surface the 

 conditions remain as they were in the smaller foetuses. In the follicles shown in the 

 figure, the ovum is seen as a large cell round which several nuclei (often showing signs 

 of division) are grouped. 



17 



