424 



DISCOVERY REPORTS 



It will be seen that the mean curve of growth rises only very gently during the earliest 

 part of gestation and is drawn, in the case of Blue whales, to begin in June. 

 Although the greater part of the curve is derived from the plotted foetal lengths, this 

 earlier part depends on the time fixed as the height of the pairing season and in order to 

 determine this time, the evidence provided by the reproductive organs may be used. 



In order to get a clear idea as to what months are most likely to be occupied by the 

 pairing season, it will be convenient to draw up a table as follows, in which the evidence 

 from the testis, the ovaries, the minute foetuses, and the growth of the larger foetuses 

 may be seen as a whole : 



Note. Owing to the relatively small number of mature whales for each month, the percentages are not 

 as reliable as one could wish. Percentages in brackets mean that there was only one mature whale in that 

 month. Column i refers to testes showing definite signs of increased activity, and column 2 refers to whales 

 in which the corpus luteum showed that ovulation must have taken place recently. In column 4 the height 

 of the curve is measured for the middle of each month, as will be seen by reference to Figs. 145 and 146. 



No column has been kept to show the monthly sizes of the ovarian follicles as the data do not lend them- 

 selves so well to treatment of this kind, but reference may be made to Fig. 124 on p. 387. 



It will be seen from the table that the testes in both species begin to show signs of 

 activity in April and continue to proliferate spermatozoa during May and probably 

 June, and that during most of the other months they are in a comparatively inactive 

 condition. In regard to ovulations the results are inconclusive in the case of Fin whales 

 owing to very limited material, but among Blue whales the majority fall in May, June 

 and July, i.e. somewhat later than the activity of the testis. The two small Blue whale 

 embr\'OS occur, as might be expected, still later (in July and August). Of the small 

 Fin whale embryos, one appears in August and the other two are aberrant. Finally, the 



