388 DISCOVERY REPORTS 



shows fine connective tissue strands radiating from the centre and dividing up the soft 

 pale bufl!" luteal tissue. In young luteal tissue the cells are vacuolated. This is illustrated 

 in Fig. 125 from a section of the corpus luteum of a whale containing a 30 mm. foetus, 

 and may be compared with the older tissue shown in Fig. 126. The mean diameter 

 of the young corpus luteum is 10-5 cm. in Fin whales and 12-7 cm. in Blue whales. 

 There is some indication that in both species it increases slightly in size up to the 

 stage when the foetus measures about i m., and then gradually becomes slightly smaller. 

 This is shown in Fig. 128 in which the sizes of the corpora lutea are plotted according 

 to the length of the foetus. It will be seen that in general the smallest corpora lutea 







* 



M 







V 



Fig. 125. Young luteal tissue from ovary of Blue Fig. 126. Older luteal tissue from ovary 



whale with 30 mm. foetus, v., vacuolated cells. of Blue whale with 6-3 m. foetus. 



of this kind were those with which no foetus was found and which were therefore either 

 corpora lutea of ovulation or corpora lutea of pregnancy which accompanied foetuses 

 so minute that they were missed. It appears that the regression in size of the corpus 

 luteum is accompanied by the disappearance of the vacuoles in the luteal cells. The 

 luteal tissue now stains intensely with Nile Blue, indicating the presence of plenty 

 of fat. 



It is difficult to say whether the size of the corpus luteum continues to decrease up 

 to the end of gestation owing to the small number of large foetuses which have been 

 recorded, but in Fin whales there seems to be a slight decrease. 



It may be mentioned here that there are invariably many enlarged follicles in the 

 ovaries of pregnant whales, and these range in magnitude from 40 mm. to 50 mm. in 

 diameter to 10 mm. and less. During lactation one or two large follicles are found but 

 the smaller ones are no longer visible. It is known that a functional corpus luteum 

 inhibits the growth of ova and the incidence of ovulation, so that the follicles seen 



