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with the anti-mes ometral wall of the uterus. This coniiectiou only 

 ends in Sciurus towards parturition, in Mus and Cavia already \'ery 

 early, in Lepus at an intermediate stage, by epithelium being pushed 

 underneath from the connecting pieces of the foetal chambers. 



In this fixation the umbilical vesicle is surrounded by proliferating 

 mucosa tissue which later degenerates and is dissolved and resorbed 

 by the ovule. The epithelium soon disappears after slight progressive 

 changes, the stroma changes into decidua by very strong proliferation 

 which in Mus, Cavia, etc. rises as reflexa round the ovule, corre- 

 sponding with the smallness of the umbilical vesicle and consequently 

 of the ovule. In accordance with an existing inclination, in the 

 order of the above mentioned series, to replace nutrition by stroma 

 products by maternal blood, the vascularisation of the decidua is 

 very small in the squirrel, very strong in Cavia and correspondingly 

 the extravasates, surrounding the ovule are very rare in Sciurus, 

 common and abundant in Mus and Cavia. 



In these processes in Sciurus maternal giant cells appear (sym- 

 plasm) and latei' foetal ones, when the former have disappeared. 

 In Lepus Schoenfeld and others found the foetal giant cells 

 (monster cells) already in earlier stages, in accordance with our 

 series; all the cells then occurring are by him considered as foetal; 

 probably, however, the maternal cells occur at the same stage and 

 part of the described cells are of maternal, symplasmatic origin. With 

 Mus both were found and distinguished by Jenkinson at much earlier 

 stages, Kolster did not see the foetal ones, Duval not the maternal 

 ones. So they must occur still earlier in Cavia; the foetal ones 

 are then probably the prolifei-ating "Gegenpolcellen" of v. Spee, 

 which perforate the zone at the vegetative pole; the matei-nal ones 

 correspond to the products of the processes in the "Implantationshof" 

 of V. Spee. Also the disappearance of these formations takes place 

 at an increasing rate (By all this it becomes clearer still that the 

 comparison of Cavia and man by v. Spee, which already from a 

 phylogenetic point of view is hazardous, must be received with caution). 



In the light of the comparative investigation these foetal "monster 

 cells" may be considered as rudiments of an organ which was 

 strongly developed in the ancestors of the Rodents. 



In Sciurus the mass surrounding the ovule ("coagulum") consists 

 especially of tissue products ; these become less prominent in the 

 order of the series and are replaced by blood. 



Of the omphaloid placentation, which in Sciurus is already rudi- 

 mentary, not much can be expected in the other members, although 

 the study (until now neglected) of the morpho logy of the extra- 



