1610 
These are his only words upon the subject in his first great 
theoretical study. It cannot be denied that they contain in no way 
‘sufficient arguments for such a radical transformation and that in 
this respect the old-fashioned explanation is more conclusive than 
the modern one.') The older conception starts from a yolkladen 
meroblastic egg. The exembryonic yolksack only serves to resorb 
the feeding material of the yolk and is shed after birth, Thus it is 
conceivable that a great amount of difference arises between the 
embryonic shield and the exembryonie part of the egg. With the 
transition of the sauropsidan oviparity into the mammalian viviparity 
the yolk material is lost, but the wall of the yolksack remains as 
the exembryonie part of the germbladder. 
I will not enter here into detailed objections to this reversion of 
the evolution. [I think it improbable that the eellbuilt germbladder 
of Mammals should have originated out of the amorphous yolk-mass 
of Sauropsida and later on I hope to demonstrate that the yolksack 
of Amphibians, the yolkmass of Sauropsida and the exembryonic 
germbladder of Mammals are not quite homologous organs, but I 
will pass on to the more synthetical part of my treatise in which 
I will try to obviate by some slight alterations the above mentioned 
objections against Husrecut’s theoretical conception. 
Like HuBrrenrT and his school, I am inclined to derive mammalian 
ontogenesis directly from the amphibian one without the inter- 
mediary of the meroblastic sauropsidan way of development, the 
latter being in my opinion far less primitive than the way in some 
Mammals. I therefore admit the secondary oviparity of Birds and 
Reptiles to have arisen out of a more primitive vivipavity of the 
Protamniota, which of course is to be derived in its turn from the 
primary oviparity of anamniote ancestors. In opposition however to 
Huprecut’s views Ll start from a yolkladen, holoblastic eggtype, 
such as is presented by the eggs of Gymnophiones and Amphiumidae. 
Fig. 1 represents a median section through a diagrammatic embryo 
of this type. The large yolksack completely divided into cells 
passes gradually into the entoderm of the intestine and shows a 
continuous ectoderm covering. The mesoderm layer of the yolk, 
which originates chiefly from the ventral blastoporal lip, the so- 
called ventral mesoderm, has not yet reached the ventral and the 
anterior side of the yolksack. The latter part of the surface of the 
1) It seems to me that the introduction of the term archomphalon by Resink 
(a somewhat modified notion of the See does not give any better solution 
of these difficulties. 
