REPRODUCTION 



373 



Figure 208. Dorsal view of uterus of pregnant 

 Bottlenose Dolphin. The foetus lies in the left 

 horn. The right horn {below) contains part of 

 the placenta alone. Note the twisted umbilical 

 cord. The ovaries are shown beneath both 

 uterine horns. {Wislocki, ifj^r.) 



The enormous intestines and other organs which are laid bare in 

 flensing big whales, often make it difficult to determine the correct 

 position of the foetus, and things are not made any easier by the flood of 

 amniotic fluid which, as in other mammals, gushes forth when the uterus 

 is dissected. (In Cetaceans, the foetal membranes are shed near the 

 cervix (Fig. 207) during birth, so that Cetaceans, unlike, for instance 

 dogs and cats, are born without them) . 



The fact that 50 per cent of seals and sea-lions are born in the same 

 position goes to confirm that our explanation of the reason for Cetaceans 

 being born tail first is correct. Now, the former have a similar uterine 

 structure to Cetaceans, the only diflference being that their foetuses (Fig. 

 210) have a very heavy and very rigid body, while their neck, head, pelvis 

 and hind limbs are extremely motile. In their case, it is therefore a matter 

 of pure chance which of these motile parts is forced towards the cervix. 



The reader may wonder whether there is no danger of the Cetacean 

 dorsal or pectoral fins catching against, for instance, the pelvic bones 

 during birth, thus causing the foetus to be stillborn or the mother to die. 

 Now, the pectoral fins lie flat against the body and their tip, at least in 

 Odontocetes, lies just in front of (and is therefore born after) the animals' 

 point of maximum girth (Fig. 210), so that the cervix and the very mobile 

 pelvis (see p. 59) are sufficiently distended to allow them to pass (Fig. 

 211). In Mysticetes, the situation is less favourable. Dunstan (1957) 

 noticed in a Humpback cow, killed while giving birth, that the pectoral 

 fins of the foetus had folded forward about the shoulder joint, but other 

 Rorqual foetuses cannot do this. Their pectoral fins, sunken in a depression 

 of the skin, are more rigid than those of Humpbacks. The dorsal fin, too. 



