380 WHALES 



breaches can only be detected by careful examination of the mammary 

 glands of all female carcasses. 



We have seen that, on either side of the genital slit, all co\vs have two 

 further openings in which the nipples are recessed (Figs. 42 and 213). 

 When air is pumped into the carcass of a Rorqual, the nipples are occasion- 

 ally forced out, and they probably do so to a lesser or greater extent 

 \vhenever a calf is being suckled. Like other male mammals, Cetacean bulls, 

 too, have a pair of small nipples, which, in their case, are set in two small 

 slits near the anus. According to Yablokov (1957), male Belugas excrete 

 a substance from their mammae which other Belugas can clearly perceive. 

 In very young (one inch long) porpoise embryos, Kiikenthal discovered 

 no less than eight rudimentary nipples, in separate groups of four on 

 either side. Six of these nipples subsequently disappear and a single pair is 

 left. The presence of the rudimentary mammae would seem to indicate 

 that the terrestrial ancestors of Cetaceans had four pairs of nipples and 

 that they were probably multiparous. 



Cetaceans have no protruding udders like cows, and their mammary 

 glands are two long, fairly small, and fairly flat organs, which are inclined 

 to each other at a slight angle (Fig. 213). Their tips are generally not far 

 from the umbilicus, and their average dimensions in 'resting' Rorqual 

 cows are about 7 feet by 2 feet 6 inches by 2j inches. During lactation, 

 their thickness increases from 2j inches to a maximum of one foot, and their 

 colour changes from pink to golden brown. If the glands are strongly 

 distended, the nipples can be seen from the outside. 



Each mammary gland is divided into countless lobes and lobules, all 

 of which lead by narrow ducts into a central lactiferous duct, which 

 becomes strongly distended close to the nipple (Fig. 214). In Cetaceans, 

 this duct may be compared with the cistern in a cow's udder, by which the 

 cow accumulates suflicient milk to be able to pour it into the suckling 

 calf's mouth. In whales, similar jets of milk often shoot from the nipples 

 of carcasses, when whalers call them 'milk-filled' - generally a reliable 

 criterion that the animal was lactating. Now, lactation means that the 

 secretory cells of the gland are producing milk, which generally indicates 

 that the cow was accompanied by a calf and that a breach of international 

 agreements has been committed. 



An inspector will therefore have to report the crew, even though the 

 cow may have been shot in good faith, i.e. even though the calf was some 

 distance away and the gunner failed to spot it, or even though the calf 

 had been weaned shortly before. This may lead to unnecessary recrimina- 

 tions, and, to avoid these, the Dutch Whale Research Group T.N.O. 

 began a detailed histological study of the mammary glands of Blue and 

 Fin Whales in 1947, using material collected on board Dutch, British and 



