Pe 
Those who maintain the first view look on the development of the 
mesoblast in Amphioxus as presenting the mode typical of the 
Vertebrata, while those who take the second view must necessarily 
regard Am phioxus as showing abnormalities in this respect. Among 
recent writers known to me who have upheld the second view are 
O. SCHULTzZE !) and CHARLES SEDGWICK Mrnor?). The latter goes so 
far as to declare, that there is probably hardly another fact in em- 
bryology so certainly established by innumerable observations as the 
fact that the vertebrate mesoderm arises as a single axial structure 
eh 6=-p: 901). 
A few years ago, Mr. IsHmkawa and myself published a joint 
paper ?) embodying the results of our observations on the formation 
of the germinal layers in Trionyx japonicus. In it, we ven- 
tured to maintain among other points that the mesoblast arises as 
paired masses in front of the dorsal lip of the blastopore, thus 
confirming the views of BALFOUR, Hertwic and others. For the 
grounds of our views, the reader is referred to the original article. 
Recently I have had an opportunity of studying the development 
of the germinal layers in another Chelonian, Clemmys japonica. 
It is in all essential respects like Trionyx, but in many points, 
the facts on which we based our conclusions in our study of Tri- 
onyx are brought out more clearly and forcibly. I wish especially to 
call attention to one point, brought ont by the present investigation, 
which I venture to think, is of more than usual interest. In a Clem- 
mys embryo of a little over three days (of about the age figured in 
Fig. 1 of my recent paper‘) and somewhat younger than Fig. 4 of 
my Trionyx paper) I obtained from the head-region some significant 
sections one of which is given in the adjoined figure. The darm- 
entoblast on each side, instead of being continuous with the 
chorda-entoblast, turns suddenly dorsalward at some distance 
from the median line and becomes continuous with the mesoblastic 
mass. The chorda-entoblast occupies the median line and on 
1) Die Entwickelung der Keimblätter und der Chorda dorsalis von 
Rana fusca, Zeitschr. f. wiss. Zool., Bd. 47. 
2) The Concrescence Theory of the Vertebrate Embryo, American 
Naturalist, Vol. XXIV. 
3) On the Formation of the Germinal Layers in Chelonia, Quart. 
Jour. Mic. Se., Vol. XXVII. Also: Jour. of Sci. Coll., Imp. Univ. Japan, 
Vol. I. 
4) On the Foetal Membranes of Chelonia, Jour. of Science College, 
Imp. Univ. Tokyo Japan, Vol. IV, pt. I. 
