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the number, and the distribution of the oil-drops in the yolk, in the 
character of the egg-capsule and in different characters of the more 
developed embryos. These eggs however were very rare and could 
only be secured in small numbers. 
The processes of development which I am about to describe in this 
paper, were studied therefore exclusively on the eggs of the spp. 
RAFFAELE already described. My efforts to keep the fry alive more 
than a few days after the yolk had been absorbed, being unsuccessful, 
I could not identify distinct species of larvae with distinct spp. of 
Muraenoids. 
I therefore will follow the example of RAFFAELE, and write 
Muraenoid N°. 1, Mur. NO. 2 etc. Mur. N°. 1 is his spec. 6, Mur. 
N°. 2 his spec. 7 etc. 
In describing the development of the entoderm and Kuprrer’s 
vesicle, I will begin by calling attention to the paper by F. B. 
SUMNER on KUPFFER’s vesicle and its relation to gastrulation and 
concrescense, published last year. 
SUMNER maintains that Kuprrer’s vesicle in Teleosts and Ganoïds 
(Amia) is formed by a solid or hollow invagination of the super- 
ficial layer (,,.Deckschicht’’). Before the closure of the blastopore the 
superficial layer by proliferation of its cells forms a thickening at 
the hind part of the embryo, that Sumner called the prostomal 
thickening in connection with Kuprrer’s theory of gastrulation in 
Teleosts. In Muraenoid eggs, of which he could study some stages, 
he found a material in which the process was to be followed „with 
almost diagrammatic distinctness’. But being short of Muraenoid 
material he could not determine accurately the relations between the 
prostomal thickening and the entoderm. From one of his drawings 
(page 60 cross section of a young Noturus embryo) seems to follow, 
that he thinks it probable, that chorda and mesoderm are derived 
from the entoderm and that the entoderm is formed at least partially 
from the proliferation of the superficial layer. 
Having an abundance of Muraenoid eggs to study, I was able to 
follow the entire process and obtained the following results : as soon 
as — the cleavage-process being ended — the cells at the blasto- 
dermmargin begin to invaginate inward, the cells of the superficial 
layer, which everywhere else are flat and do not partake of the 
invagination process, begin to increase in size at one point. This 
increase of size of the cells of the ,Deckschicht” is limited to a 
small area at the hind end of the thickening of the blastoderm, which 
is the first indication of the embryonic shield. There, at the edge of 
the blastodermring, the cells of the superficial layer thicken, become 
