ï62 



WHALES 



Figure 201. Pregnant uterus of a Common 

 Porpoise seen from beneath. The embryo is in 

 the left uterine horn, while the right horn 

 contains the aUantois {one of the two em- 

 bryonic membranes) which f arms part of the 

 porpoise's placenta. Note the short umbilical 

 cord. {Wislocki, 1933.) 



litter would have been viable, but in any case, while sextuplets have also 

 been described in cattle, horses have never been known to produce more 

 than four foals simultaneously. (Man holds the record with octuplets.) 



The Cetacean placenta, i.e. the tissue by which the embryo is attached 

 to the wall of the uterus, is called diffuse and epithelio-chorial, by which 

 biologists mean that it is uniformly distributed across the inner walls of 

 both uterine horns and that maternal and foetal tissues do not become 

 fused, their respective vascular systems being separated by two capillary 

 walls and two epithelial layers. Because of this separation, whales lose less 

 blood when they give birth than, for instance, human beings in whom there 

 is a much more intimate association between the two tissues and a con- 

 sequent laceration when they are separated at birth. Nevertheless, slight 

 bleeding at birth has been observed in a Bottlenose Dolphin at Marine- 

 land, due to the fact that foetal and maternal tissue adhere in such a way 

 that when they are separated some damage is unavoidable. Slight bleeding 

 also occurs in horses, pigs and camels which have the same type of 

 placenta. 



Unlike man, whose embryo is surrounded with an amnion alone, 

 Cetaceans (like Ungulates and Carnivores) have two embryonic mem- 

 branes both filled with fluids: the amnion which surrounds the embryo 

 and the allantois which lies outside. While a small part of the aUantois 

 is geneially found in the uterine horn containing the embryo and the 



