444 THE PHYSIOLOGY OF REPRODUCTION 



some of the superficial capillaries miliary haemorrhages occur (see 

 Chapter ILL). 



At the beginning of pregnancy, blood effusions are found close 

 under the surface of the mucous membrane, but bleeding into the 

 uterine cavity, which took place during the procestrum, has entirely 

 ceased. The epithelium of the surface glands and crypts is swollen 

 and pervaded with minute fat globules in the dog (Bonnet x ) and cat 

 (Melissenos 2 ). The glands widen quickly into "chambers," and 

 tracts of their proliferated epithelium are invaginated, and often 

 obliterate the lumen. The widening of the glands and crypts makes 

 the deep layer spongy. The capillaries increase and form practically 

 the whole of the sub-epithelial layer. Immediately below it lies the 

 layer of glandular ducts which are obliterated by debris resulting from 

 the degeneration of the proliferated epithelial cells. Between it and 

 the spongy layer is the compact layer, also formed from the sub- 

 epithelial layer. In it the glands are not so widely dilated and the 

 connective tissue is more abundant (Fig. 122). 



The embryotrophe at this stage differs from that in Ungulates. 

 The glandular secretion is less fluid, perhaps because the lymph 

 transudate is less abundant (Kolster 3 ). It surrounds the ovum to 

 form the prochorion or " Gallertschicht," and is, according to Bonnet, 4 

 absorbed by the trophoblast. 



When the prochoriou disappears, the foetal ectoderm already has 

 proliferated over a broad zone of the citron-shaped ovum (Fig. 123), 

 to form villosities which attack the surface of the mucosa, and obtain 

 an attachment to it about the twentieth day in the dog (Duval 5 ) 

 and the twelfth day in the cat (Robinson). Vascular processes of the 

 allantois grow into the centre of the trophoblastic villi, first 'over a 

 limited discoid area, and later over the whole zone as the allantois 

 spreads round the wall. Hence the rudimentary placenta is discoid 

 and the completed placenta zonary. 



In procuring attachment to the uterus many of the villi project 

 into glands and crypts. According to Strahl, 6 the epithelium lining 

 the ducts and the surface of the uterine cavity is then transformed 

 into a syncytiurn and invests the villi externally. Heinricius 7 is of 



1 Bonnet, "Beitrage zur Embryologie des Hundes," Anat. Jfefte, vol. xx., 1902. 



2 Melissenos, " Ueber die Fettkbrnchen und ihre Bedeutung in der Placenta 

 bei den Nagern und der Katze," Arch. f. mikr. Anat., vol. Ixvii., 1906. 



3 Kolster, " Ueber die Zusammensetzung der Embryotrophe der Wirbel- 

 thiere," Ergebn. d. Anat., vol. xvi., 1906. 



4 Bonnet, "Ueber das 'Prochorion' des Hundekeimblase," Anat. Anzeig., vol. 

 xiii., 1897. 



5 Duval, "Le Placenta des Carnassiers," Jour, de I' Anat. et de la Phys., 1893. 



6 Strahl, " Die histologischen Veranderungen d. Uterusepithel. in d. Raub- 

 thierplacenta," Arch. f. Anat. u. Phys., Supplement, 1890. 



7 Heinricius, " Ueber die Entwicklung und Struktur der Placenta beim 

 Hunde," Arch. f. mikr. Anat., vol. xxxiii., 1889. 



