47^ THE PHYSIOLOGY OF REPRODUCTION 



tions have been made regarding the metabolism of iron-containing 

 substances. 



<iuima-Pig. In the guinea-pig the ovum is again completely 

 surrounded by decidua. Reichert l was the first to notice that the 

 ovum lay in a special cavity, " a little nest." Bischoft' 2 stated that 

 the nest was only temporary, and the ovum again appeared in the 

 uterine cavity, only that part of the nest remaining which formed 

 the placenta. After a long interval this was proved to be wrong by 

 Reichert 3 and Hensen. 4 



The fertilised ovum reaches the uterus as a niorula or early blasto- 

 cyst, surrounded by the zona radiata. On the seventh day the zona 



FIG. 134. Longitudinal section of the uterus and implantation cavity of the 

 guinea-pig. (From Duval's "Le Placenta des Rongeurs," Journ. de FAnat. 

 et de la I'/iys., 1892.) 



ine#, Mesometrial border ; gl, uterine glands ; /, uterine lumen ; 

 W, blastodermic vesicle. 



disappears and embedding begins, but even before this, according to 

 von Spee, 5 the ovum is fiied by processes which extend from the cells 

 of the implantation pole through the zona and come into direct 

 metabolic relationship with the epithelial cells. As in the mouse, 

 the blastocyst remains small, about one-tenth of a millimetre in 

 diameter. At its point of contact with the mucosa, the epithelium is 

 rapidly eroded, and absorbed along with its fat globules by the foftal 

 ectoderm. At the same time changes occur in the deeper layers. In 



1 Reichert, " Ueber die Bildung der hinfiilligen Haute der Grebarm utter," 

 Miller's Arch., 1848. 



2 Bischoff, Entivicklung des Meerschweinchens, 1852. 



3 Reichert, "Beitrage zur Entwicklungsgeschichte des Meerschweinchens," 

 Abhandl. d. Akad. d. Wissensch. zu Berlin, 1861. 



4 Hensen, " Beobachtungen iiber die Befruchtung und Entwicklung d-s 

 Kaninchens und Meerschweinchens," Zeit. f. Anat. u. Entu'ick., vol. i., I860. 



6 Von Spec, "Die Implantation des Meerschweincheneies in die 'Uterus- 

 wand," Zeit. f. ^forphoL u. Anthropol., vol. iii., 1901. 



