86 DISCOVERY REPORTS 



when they become adult. The blubber of South African and South Georgian Hump- 

 backs, unlike that of the whales of genus Balaenoptera, differs little in thickness. Preg- 

 nant whales, also, have blubber above the average in thickness. A decrease in blubber 

 thickness is found at the end of the whaling seasons both at South Georgia and South 

 Africa. 



The external parasites of Humpback whales are Paracyamiis, Coronida and Concho- 

 derma, all of which are usually present. Several species of diatom, including Cocconeis 

 wheeleri which has not been found on other whales, occurred sparingly in patches on the 

 surface of the skin. 



Only one Humpback contained intestinal parasites — a species of nematode worm. 

 Another species of nematode, however, occurs commonly in the kidney and is also 

 sometimes found in the urethra of males. 



The external and internal genitalia of both sexes are described. The histological state 

 of the testes was examined in nine whales and the results indicate a male sexual season 

 occurring between March and December. 



Dated records of foetal lengths show that the period of gestation is about eleven 

 months and that the young are born at a length of about 4-5-5 m. Lactation lasts about 

 five months and weaning takes place when the calf is about 7-5-8 m. in length. 



The main part of the pairing season occurs from August to November, with its peak 

 in September: consequently most births take place from July to September with a 

 maximum in August. A few pregnancies, however, start in all months of the year, 

 showing that oestrus may occur outside the main breeding season. 



The results of a detailed examination of the internal genitalia of nineteen female 

 Humpbacks are given in full. From these, and other data, it is concluded that the 

 species breeds usually once every two years, but that occasionally, when a whale breeds 

 early in the season, an extra pregnancy is interpolated in the normal cycle so that two 

 pregnancies occur in three years. 



The numbers of old corpora lutea in the ovaries indicate a polyoestrous sexual cycle 

 with an average of four dioestrous cycles and five ovulations at each cycle succeeding 

 the first. 



Sexual maturity is reached at an age of twenty to twenty-two months and breeding 

 first occurs at the end of the second year after the birth of the whale. Physical maturity, 

 as shown by ankylosis of the epiphyses of the vertebral column, is reached at or before 

 the age of ten years. The recovery of an identifiable harpoon shows that Humpback 

 whales can reach an age of at least eighteen years. 



Logarithmic plotting of mean values of body measurements against total length shows 

 that the growth rates of the various parts of the body increase with increasing body 

 length from the posterior towards the anterior end. It is therefore suggested that the 

 whole growth of the whale is mainly directed towards development of the feeding 

 mechanism, represented by the baleen and mouth. One measurement, the genito-anal 

 distance of the female, is found to decrease not only relatively, but absolutely, with in- 

 creasing body length. 



