1614 
the resorption of the jelly eggeoverings, and therefore we may use 
here without restrictions the term diplotrophoblast of Husrecut to 
which this organ answers morphologically and physiologically. 
But evolution *) does not stop at this point: 
After resorption of the tertiary eggmembranes direct osmotic inter- 
change of gasses and dissolved materials between foetal and maternal 
blood becomes possible and this method of respiration will be much 
more intense than the interchange between the aereal content of the 
oviduct and the foetal blood, which is obliged to pass the eggmem- 
branes and the liquid of the eggchamber. Development therefore will 
show a tendency to secure as soon as possible the contact of diplo- 
trophoblast and uterine wall. Thus this respiratory embryonic append- 
age will be precociously segregated *) and the tertiary eggcoverings 
will show a tendency to be reduced and to disappear. But then 
the eggchamber loses its significance as protective watereushion in 
which the embryo may develop under uniform pressure and it will 
be necessary to transfer this function to another organ. 
Before treating this question further I must call the attention to 
the fact that by the precocious segregation of the diplotrophoblast 
the conditions of the fruitbladder in a hypothetical protamniote very 
much resemble those of the early mamuinalian fruitbladder (see fig. 2). 
On tbe ventral side of the vesicle a large watercushion is present, 
the wall of which shows all sorts of folds and proliferations and 
possesses respiratory and nutritive functions, while the still small 
embryonic area is situated on the dorsal surface of the fruitbladder. 
The comparatively large yolksack is attached to the ventral side 
of the embryonic area and is connected with the surface of the 
exembryonic fruitbladder by the proamnion-area. *) 
As the diplotrophoblast has only significance as an embryonic 
organ for respiration and nutrition, it is shed or resorbed at birth 
1) For convenience sake I use in this paper the Neo-Lamarckian mode of 
expression, without assuming the Neo-Lamarckian mode of explanation with all its 
inferences. 
2) The mesodermal covering of the diplotrophoblast arises out of the ventral 
mesoderm. In consequence this also will show a tendency to precocious segregation. 
Sometimes it appears even before there is question of mesodermformation in the 
embryo proper. In some orders of Mammals (SCHLATER. Anat. Anz. Bd. 30 and 
31, 1907) e.g. in Primates, but especially in polyembryonic armadillos (PATTERSON, 
Anat. Anz. Bd. 41, 1912) this phenomenon is most striking. 
3) Since the proamnion-area does not possess a mesodermal covering, it cannot 
perform any respiratory function and it cannot be divided into a somatic and a 
splanchnic yolk sheet. Hence the yolk sack will be connected with the surface of 
the fruitbladder at this spot, 
