360 THE PHYSIOLOGY OF REPRODUCTION 



maternal layer. Langhans l regarded the spaces as formed 

 by that part of the lumen of the uterus which lay between the 

 surface of the mucosa and the chorion, and thought that the 

 villi by eroding vessels came to be bathed in extravasations of 

 maternal blood. Klebs 2 considered them to be lymph-spaces, 

 and therefore extra-vascular ; and Jassinsky 3 described them as 

 being formed by the penetration of the villi into the maternal 

 glands, whose epithelium came to clothe the villi externally. 

 Now it has been proved from the examination of early ova 

 that the intervillous spaces are entirely foetal and are formed 

 in the epiblast. 



The investigations of Langhans proved to be the turning- 

 point in the controversy regarding the investment of the villi. 

 He showed that it consisted in the earlier stages of pregnancy 

 of a double covering, a deep layer of cells (Langhans' layer), 

 and superficially a mass of " canalised fibrin." The presence 

 of fibrin had been noted by Weber and several of his successors ; 

 Winkler 4 proved it to be a constant phenomenon, and gave it 

 the name " Schlussplatte " ; but it was Langhans who first de- 

 scribed its relations, and suggested its probable origin from the 

 foetal epiblast. The cellular layer, according to Langhans, was 

 mesoblastic. Kastschenko 5 first described both layers as 

 epiblastic, and showed that the outer layer was a syncytium, 

 or mass of nucleated protoplasm without cell-boundaries. Such 

 investigations led to the feeling that the structure of the placenta 

 could only be understood by tracing its development from very 

 early periods of gestation. Hence the search for and examina- 

 tion of young human ova were stimulated, and the study of the 

 uterine condition in age-series of pregnant animals was begun. 

 Up to this time the chief controversies had raged around the 

 human placenta. Comparative placentation had engaged the 



1 Langhans, " Untersuchungen iiber die menschliche Placenta," Arch, 

 f. Anal. u. Physiol., anat. Abth., 1877. 



2 Klebs (E.), " Zur vergleichende Anatomie der Placenta," Arch. f. mikr. 

 Anat., vol. xxxvii., 1891. 



3 Jassinsky, " Zur Lehre iiber die Struktur der Placenta," Virchow's 

 Arch., vol. xl., 1867. 



4 Winkler (F. N.), "Zur Kenntnis der menschlichen Placenta," Arch. f. 

 Gynak., vol. iv., 1872. 



6 Kastschenko, "Das menschlicbe Chorionepithel und dessen Rolle bei 

 der Histogenese der Placenta," Arch. f. Anat. u. Phys., anat. Abth., 1885. 



