No. 2.] DEVELOPMENT OF MANICINA AREOLATA. 237 
as far as the left halves of the sections are concerned, they are 
identical in all essential respects. In each the cesophagus is 
opposed to the surface ectoderm along -the meridians of two 
adjacent mesenteries (a and 4, I and 3), and also over the interven- 
ing tract. In a later stage an endoderm lobe grows up between 
aand 6 in Fig. 30, and between I and 3 in the woodcut, and in 
each this lobe becomes an intermesenteric chamber. If, now, 
in the larva, Figs. 30-33, the right side had followed the exam- 
ple of the left, that is, if the second and fourth mesenteries had 
been formed in the same manner as the first and third (@ and 8), 
there would have resulted an exact counterpart of the condition 
in the Aurela larva. 
The four mesenteries of Scyphostoma would thus seem to 
correspond to the first and second pairs of mesenteries in 
Manicina. We may suppose that in the primitive Scyphostoma 
the mesenteries were usually formed in the gradual way which 
is normal in Manzczna, but that the Scyphostoma had inherited 
from the parent stock (probably Anthozoa with a large number 
of mesenteries) a tendency towards the variation illustrated in 
Figs. 30-33, and that this variation gained ground and finally 
became the normal process. There is, of course, an alternative 
to this hypothesis, namely, to regard the variation found in 
Manicina as a case of partial reversion to the ancestral condition 
as presented by Aurelia. But the derivation of the Anthozoa 
from such an ancestor as the young Scyphostoma (or Scyphula 
with four endoderm lobes) is beset with the greatest difficulties ; 
for instance, the formation of the first before the second mes- 
entery, and the very general occurrence of a primary tentacle 
in actinia larvae and in the Scyphostoma itself. Moreover, the 
Scyphula larva has not been found in any Anthozoa, unless, 
indeed, the case of Cerianthus be really, as Professor Géotte 
seems to have considered it, similar to Aurelia. 
Having shown that it is possible to derive the so-called Scy- 
phula larva from the larva of Manicina, and that it is conse- 
quently in all probability an instance of secondarily acquired 
symmetry, I consider Gétte’s objection, based on the existence 
of this larva, to the hydropolyp ancestry of the Anthozoa, as no 
longer valid. The question whether or not the Anthozoa are 
descended from hydropolyps must be argued out on the ground 
of some more primitive Anthozoan development, such as that 
