410 THE PHYSIOLOGY OF REPRODUCTION 



Ttirsius approaches more closely to the Insectivora and Primates. 

 The trophoblast proliferates and penetrates into the mucosa, 

 and maternal blood circulates in its spaces. The mesoblast 

 grows profusely, and forms with the trophoblast a true chorion 

 in Hubrecht's restricted sense. The placenta is discoid. In 

 Galago agisymbanus, Strahl l has shown that a layer of secretion 

 lies between the uterus and the ovum from the beginning of 

 pregnancy. It is absorbed by the ectoderm, the cells of which 

 are vesiculated over the gland orifices. Many blood extravasa- 

 tions occur in the connective tissue of the mucosa, and the red 

 blood corpuscles undergo changes as in the sheep, the glandular 

 cells and embryotrophe containing granules which give an iron 

 reaction. Turner 2 had previously noted in lemurs the intense 

 brown staining of the glands from effused blood. 



CETACEA, EDENTATA, and SIRENIA. The details of placental 

 development and the constitution of the embryotrophe are 

 unknown. 



IV. THE PLACENTA IN DECIDUATA 



In the Deciduata three modes of attachment between embryo 

 and mother are found : Centric, in which the blastocyst rests in 

 the cavity of the uterus, attains a large size, and comes in con- 

 tact with the wall over its whole circumference ; Excentric, in 

 which the blastocyst remains smalland lodges in a furrow of 

 the uterine mucosa, and later a decidua reflexa is formed ; 

 Interstitial, in which the small blastocyst attacks the mucosa 

 at one point and reaches the connective tissue. In this form 

 also a decidua reflexa is formed. 



In the neighbourhood of the attachment the mucosa de- 

 generates, but the connective tissue cells usually enlarge to 

 form decidual cells before degeneration sets in. The capillaries 

 dilate and come in contact with the trophoblast. The mucosa 

 interlocks so closely with the foetal villi that the two tissues 

 cannot be separated without injury. 



1 Strahl, " Die Verarbeitung von Blutextravasaten durch Uterindriisen," 

 Anat. Anzeig., vol. xvi., 1899. 



2 Turner, " The Placentation of Lemurs," Jour, of Anat. and Phys., 

 vol. xiL, 1878. 



