422 



DISCOVERY REPORTS 



It is now seen that the time of ripening of the ovarian folhcles, the occurrence 

 of corpora lutea resuking from recent ovulations, the occurrence of minute foetuses, 

 and the season at which the testis shows an increased activity, all point to the earlier 

 part of the southern winter as the season at which the breeding processes become 

 general. The next step will be to examine the records of the lengths of the foetuses at 

 different times of year and to construct curves to represent the growth of the foetus. 

 The pairing season, as indicated by these curves, may then be compared with informa- 

 tion provided by the reproductive organs. 



The total number of foetuses examined at South Georgia and Saldanha Bay is as 

 follows : 



In the above list twins (which have occurred twice) are counted as two foetuses. 

 Cases in which foetuses were known to have been present (e.g. by traces of foetal 

 membranes), but were not found, are not included. Those recorded under "Sex not 

 determined" were either too small or too much decomposed for their sex to be dis- 

 tinguished. 



In Fig. 145 all the Blue whale foetuses which have been examined in the course 

 of the work are plotted according to their lengths and the dates on which they were 

 found. The average monthly lengths are also shown. 



The curve is an attempt to show what is the probable rate of growth of the foetus. 

 So far as its actual shape is concerned, it should represent the growth of any Blue whale 

 foetus, while its position in respect to the time of year should enable one to find the 

 probable mean size of all the foetuses at a given time. The curve in this case is drawn 

 "freehand" to represent as well as possible the general trend of the mass of plotted 

 points, regard being paid also to the monthly average lengths. It is not, of course, intended 

 as a final representation of the rate of growth, but simply what seems most probable 

 from the given material. A similar curve for Fin whales is shown in Fig. 146. Here the 

 plotted points have turned out to be considerably more scattered than in the case of 

 Blue whales, though the monthly average lengths arrange themselves in a fairly good 

 line. One foetus, measuring 5 m. in November, lay far outside all the others and is 

 not shown in the figure. This one, however, was an abortive foetus found in whale 

 No. 262. It was a case of abdominal pregnancy and when found the foetus was in a 

 degenerate condition and appeared to be in the process of reabsorption by the parent. 

 It may therefore be left out of any calculations concerned with the growth of the foetus. 



