134 



DISCOVERY REPORTS 



female pregnant with a foetus 2-6 m. long the pregnant cornu was 54 cm. across and 

 the non-pregnant one 49 cm. These figures give an average of about 17-5 cm. as the 

 width across the uterus in ovulating whales, and some 5 cm. less in the resting state. 

 Mammary glands. The mammary glands are situated on each side of the median line, 

 with the nipples rather under 0-2 m. to each side of the vulvo-anal groove. Only one 

 whale was examined in which lactation was actively taking place ; in all others the gland 

 was either involuted or near the end of lactation. Table IX shows the thickness of the 

 gland in the specimens measured. The involuted mammary gland thus varies from 5 

 to 12 cm. in thickness. In only one of the whales with non-involuted mammary 

 glands was lactation more than slight, but in them the thickness was also from 5 to 

 12 cm. The involuted gland in Fin and Blue whales is from 5 to 10 cm. thick, and in 

 full lactation it is 15-30 cm. When the small size of the female Sperm whale is taken into 

 consideration (none of these whales measured more than 11-3 m. long, the average 

 length being lo-i m.) the size of the mammary gland in proportion to the size of the 

 body is seen to be very large when compared with the former species. The Sperm whale 

 therefore resembles the Humpback whale in the comparatively large size of the mam- 

 mary gland, which one presumes gives a correspondingly large quantity of milk when 

 in full lactation. 



Table IX. Sperm whale. Thickness of mammary gland 



Table IX shows also that the end of lactation frequently overlaps the beginning of the 

 next sexual cycle and may even continue into the beginning of the next pregnancy. This 

 may be compared with the events found in Blue and Fin whales in which there appears 

 to be a definite resting period between the end of lactation and the beginning of the next 

 sexual cycle. 



Gestation and breeding season. There are in the British Museum (Natural History) the 



