198 HIROSHI OHSHIMA 
My own observation on the specimens of C. plancei brought 
back from Naples by the late Professor Mitsukuri shows 
clearly that the archenteron is twisted exactly in the same 
manner as in C©.echinata. It seems to me highly probable 
that Selenka’s figure (Pl. xl, fig. 21) was obtained from 
a thick section, as he was apparently unable to get a good 
series of well-orientated sections. His figure is said to represent 
a sagittal section, but really it is a frontal one. From Newth’s 
figure of a longitudinal section of a forty-fourth-hour gastrula of 
C.normani (PI. 8, fig. 8) it is obvious that the archenteron 
is not simply folded in an S-shape, but is twisted in a spiral. 
The figure, too, is a frontal section, I believe, not a sagittal one 
as he supposed. 
It was found by Edwards (12, p. 213) in Holothuria 
floridana that by the twenty-second hour a plug of cells 
crows out from the blind end of the archenteron towards the 
blastopore, and that by this plug the archenteron is divided 
into the dorsal and ventral branches. No such changes were 
observed by Selenka n H. tubulosa. 
In C. plancei the position of the blastopore changes, accord- 
to Selenka, shghtly towards the future dorsal side, but 
according to Ludwig it is said to shift ventrad. I could 
not decide which of the two holds true in my case. In most 
cases the blastopore opens at the hind end. 
Stomodaeum. The stomodaeum makes its first appear- 
ance in the quite old gastrula, where the archenteron begins to 
divide into hydro-enterocoele and gut (PI. 8, figs. 13, 14 a, sf). 
It is preceded by a thickening of ectoderm on the ventral side 
at about the middle of the body (PI. 8, fig. 11 a, sy). This 
is partly due to a sinking down of the ectodermal cells and 
partly to an accumulation of the multiplymg mesenchyme 
cells. Here a syncytium is formed, the internal surface of the 
ectoderm not being a definite one, touching the ventral edge 
of the flattened part of the archenteron. The surface of the 
latter is still clearly cut, no mitotic figures being found on this side. 
The stomodaeal depression then comes in sight a little on the 
left side of the plane in which the flattened part of the archen- 
