( 389 ) 



placentary paris of the foctal chamber might perhaps slied liglit on 

 this subject. 



The now following appearance of the allantoic! placenta is found 

 latest in Sciurus, earliest in Cavia. The tendency, increasing in the 

 well-known order, to bring about as much as possible a nutrition 

 without tissue products of the mucosa of the uterus and an allantoidean- 

 placentary exchange between foetal and maternal blood, causes the 

 processes, playing a part in placentation, to change: in Sciurus we 

 still have a very strong hyperplasia of stroma-epitheliuni, later de- 

 generation, disintegration and resorption witli penetration of the 

 trophoblast into this mass, all temporarily clearly distinct and rela- 

 tively slow, in Cavia we fuid almost exclusively vascular proliferation, 

 while proliferation and degeneration go hand in hand and the invasion 

 of the trophoblast follows closely on these, this latter process not 

 proceeding far and being soon finished (since the object: amener une 

 hémorrhagie maternelle a ètre circonscrite par des tissus foetaux 

 (Duval), is sooner reached). In the other animals all intermediate 

 stages are found. 



The later processes in the development of the placenta are in all 

 different, although they are alike in principle: subdivision of cavities 

 respectively vessels, containing maternal and foelal blood. The allantois 

 remains passive, the foetal mass grows further and further round 

 the allantois-ramifications, as it penetrates further into the cavity of 

 the foetal chamber. 



The formation of foetal giant cells proceeds with all Rodents over 

 the whole trophoblast from the vegetative to the placentary pole; 

 also the decidual cells become larger, so that also the giant cells, 

 which in all have been found supra-placentary (as J en kinson already 

 stated for the Mouse), are partly of maternal, partly of foetal origin ; 

 with Sciurus the two always remain easy to distinguish. 



The more or less isolated place, which according to the statements 

 of authors, Lepus would in some respects occupy, will perhaps 

 disappear, when the until now somewhat neglected study of the 

 pre-placentary period will ha\e been more extensively carried out 

 (also in regai-d to the morphology of the foetal chamber). 



Finally I have not become convinced that also for the morphology 

 of the foetal chamber cavities the unity in the structural plan goes 

 for all Rodents as far as is claimed by Fleischmann ; the difference 

 in the statements I met with, will however perhaps disappear when 

 all this has been studied with the aid of a more extensive material, 

 although Fleischmann's conceptions, for similar reasons, are certainly 

 incorrect in their present shape. 



