4SO THE PHYSIOLOGY OF REPRODUCTION 



It has been shown that the fostal fat ui the dog is not necessarily 

 derived directly from fat fed to the mother, for Thiemich ^ fed a dog 

 on widely different fats (palmitin and linseed oil, etc.) during two 

 successive pregnancies but found the fat in the fojtus to be the same 

 in each case (see below, p. 543). 



Peoboscidea. — In the elephant, the allantois is large and 

 ^vesicular. Short villi are developed over a large area of the 

 blastodermic vesicle. They lodge in pre-existing depressions in the 

 uterine wall, but the trophoblast is inactive and does not attack 

 the maternal tissues (Assheton ^). Over a zonary area, however, the 

 vilK are much longer, and, penetrating deeply into the maternal 

 tissues, they form a large mass of tissue in the meshes of which 

 maternal blood circulates. Hence the zonary placenta differs from 

 that of Carnivores and resembles that of Insectivores, in which, 

 however, the maternal blood circulates in trophoblastic spaces before 

 the advent of foetal capillaries. 



Though no red blood corjauscles appear to be absorbed as siich 

 by the trophoblast, there is evidence of an active absorption of 

 haemoglobin derivatives, the presence of iron compounds being easily 

 demonstrated, especially in the cores of the villi and the walls of 

 the foetal capillaries. In the syncytial trophoblast, however, the 

 Prussian-blue test is negative (see p. 511). 



At birth the long villi are left in situ and absorbed by the 

 maternal tissues. 



Hyrax. — As in the elephant, the placenta of Hyrax has been 

 studied only in isolated specimens, and its development is not known. 

 According to Assheton,^ the trophoblast is probably thickened all 

 round the wall of the blastocyst, as in the hedgehog and man, but 

 there is no appearance of a decidua reflexa. Maternal blood is 

 carried directly to the foetal side of the trophoblast, where it is 

 close to the foetal vessels, and so may provide nutriment. It 

 then trickles back through a complicated system of lacunse in the 

 trophoblast. 



The placenta is at first diffuse and later zonary. In the mucosa 



Prussian blue in the maternal endothelium, but none ■within the ectoderm. 

 In the longer experiments blue granules had penetrated the ectodermal layer, 

 but not the fatal endothelium. The placental ectoderm thus shows- a marked 

 selective behaviour. '(Cunningham, R. G., "Studies in Placental Permeability — 

 I. The Diii'erential Resistance to Certain Solutions Offered by the Placenta in 

 the Oat," Amer. Jowr. of Physiol., vol. liii., 1920.) See also below, p. 466, footnote. 



1 Thiemich, "tjber die Herkunft des Fotalen Fettes," Zent. f. Phys., vol. xii., 

 1898. 



^ Assheton, " The Morphology of the Ungulate Placenta, with Remarks on 

 the Elephant and Hyrax" Phil. Tra-ns. Roy. Soc, London, Ser. B., vol. cxcviii., 

 1906. 



^ Assheton, loc. cit. 



