54 



DISCOVERY REPORTS 



was taken in so few mature whales. This measurement is plotted against lengths of whale 

 in Fig. 51, immature, resting, and lactating whales being separated: pregnant whales are 

 not included. This figure shows a gradual increase of width of the uterine cornua with 

 increasing body length, and an indication is given of the increased rate of growth as 

 sexual maturity is reached at a length between 12 and 13 m. No material from Hump- 

 backs is available for an examination of the uterine mucosa, but there is no reason for 

 thinking that it is different in kind from that established as occurring in Blue and Fin 

 whales. 



Mammary glands. The mammary glands, as in all Balaenopterids, are situated under 

 the blubber on each side of the middle line just anterior to the reproductive aperture, so 

 that their posterior ends and the teats lie alongside it. Few measurements of the gland 



30- 



a 



c 



3 

 c 



(_ 



o 



LJ 

 QJ 



C 



o 



sz 



20- 



10- 



i=: 0- 



• Immature 

 o Ovulating- 

 ® Resting 

 D Lactating 



® 



• •• • 



* 



12 



14 



10 11 12 13 



Total Length in metres 



Fig. 51. Humpback whale. Females. Variation in size of uterus. 



are available from mature whales, but Fig. 52 summarizes the observations recorded. 

 Here the thickness of the gland at its widest part is plotted against the length of the 

 whale, four states of the gland being recognized: non-parous, resting, intermediate, and 

 lactating. The non-parous class includes both immature whales and whales that have 

 recently become mature and are pregnant for the first time, but in which the gland has 

 never lactated. It will be seen that the thickness of the gland in this class varies between 

 2 cm. and just under 5 cm., with possibly a slight tendency towards the higher values 

 with increasing length of body. This thickness is greater than that found in Fin and 

 Blue whales, in which the immature gland is not usually over 2 cm. thick at its widest 

 part. The resting class consists of those which have lactated but in which the gland is 

 involuted and not active. In this class it varies between 5 and 10 cm. in thickness, again 

 a greater thickness than that found in corresponding Fin and Blue whales, where the 

 resting gland is 5-6 cm. deep. The intermediate class contains those whales in which 

 the gland is becoming active preparatory to lactation just before parturition, or in which 

 it has not quite reached the resting stage towards the end of the lengthy period of in- 

 volution. Only one whale is here placed in that class, and it is referred to it with some 

 doubt, as although it is noted that the gland contained no milk, but a brown sticky fluid, 



