joa CHARLES W. HARGITT 
law. Granted the diploblastic character of coelenterate and 
sponge; granted further, the gastrula stage in ontogeny through- 
out a large proportion of higher Metazoa, who could well resist 
the conclusion jumped at by Haeckel as to the necessary homology 
of gastrula and planula, facts to the contrary notwithstanding! 
c. The morula. It has just been stated that the planula is 
the distinctive larva of coelenterates. Another ontogenetic 
stage, however, must not be overlooked, namely, the morula. 
Of this one hears little now-a-days, though formerly it was a name 
fairly common in the literature of embryology. Even so recent 
a text-book as that of Korschelt and Heider devotes to it a single 
brief paragraph or so. They remark, ‘‘we shall see that examples 
of such a mode of origin of the two primary germ-layers are still 
ascribed to many Hydroids and Anthozoa, though probably the 
greater part of the cases referred to this: method can be reduced 
to epibolic gastrulation, in which events the morula stage, as being 
a schema founded on erroneous assumptions, would have to be 
omitted.” As an illustration of subserviency to dominant 
theory this sentence is a brilliant example! As a matter of fact 
epibolic gastrulation is absolutely unknown in coelenterate devel- 
opment, cases given of its occurrence having, without exception 
been proven egregious errors. 
It might be questioned whether the morula, as a stage, should 
be given recognition. But when it is taken as the counterpart 
of the blastula, a stage everywhere recognized, but comparatively 
rare in the phylum under review, the objection vanished. The 
morulaisfarand away the dominant cleavage embryo in Hydrozoa 
and common in other classes, the Scyphozoa alone excepted. 
Accounts of its structure and origin given in an earlier section 
obviate any call for details here. Suffice it to say, that the com- 
plicated methods described by Metschnikoff (’86, p. 70), while 
interesting and ingenious, are but of small value. That delam- 
ination and immigration (polar or multipolar), may occur need 
not be questioned; but that they occur in any such degree of fre- 
quency or constancy as to constitute laws of entoderm formation 
none who has had to do with the problem would hesitate to deny. 
While less importance is attached to this problem of germ layers 
