122 BULLETIN OF THE 
reach such different conclusions as those published by Claus (’83 and 
90) and Goette (87), concerning the method of gastrulation in the 
same animal, A. aurita. Since studying this process in A. flavidula, it 
seems less strange. The results obtained from my first sections led me 
to think that the conclusions reached by Goette would be confirmed in 
the case of A. flavidula. Better staining, thinner sections, and more 
accurate orientation have made it certain, however, that the method of 
gastrulation in this species is much more in accord with the description 
given by Claus, and that the process really is one of invagination. 
Certain considerations weaken my confidence in the position defended 
by Goette. A comparison of his Figures 6-9 (’87, Taf. I.) with some 
of my thicker sections, or with those which were made when the gastrula 
was go oriented as not to be cut parallel to the blastoporic canal, makes 
it appear, to me probable that his results are based upon similar inade- 
quate sections, In Figure 8 (Plate IL) there are only about one half 
as many nuclei visible as there are cells, the nuclei of a portion of the 
cells being contained in adjacent sections. In figures of corresponding 
stages of A. aurita as represented by Goette (’87, Taf. I.), nuclei are 
figured in nearly all the cells. I believe this to be evidence that his 
figures were drawn from thick sections. The blastopore, because of its 
very small diameter, is quite easily overlooked in thick sections, and 
especially if the plane of sectioning is somewhat oblique to the longitu- 
dinal axis of the blastopore. Since, as previously stated, the nuclei of 
the entodermal cells are usually situated in the portion of the cell near- 
est the ewlenteron, it is easy to find in thick sections of an in yaginating 
embryo conditions like those represented by Goette in his Figures 6-8, 
My Figure 12 (Plate II.) reproduces a section of the same series as 
that represented in Figure 3 (Plate I). The intervening section (not 
figured) is quite similar to Goette’s Figure 8. An examination of the 
cells bordering the blastoporie canal in Figure 3 will show how sections 
like Figure 12, or such as are a little oblique to the chief axis of the 
embryo have the appearance of containing immigrating cells, Such 
sections also exhibit the flattening in the region of the shorter cells to 
which Goette (’87, p. 4) has called attention in the following words : 
«Schon während der Gastrulation zeigt sich eine Stelle des Keims im 
Bereich seiner kürzeren Zellen etwas abgeplattet.” 
Additional considerations increase the probability of the correctness 
of the view which I have advanced to explain Goette’s error. With 
advancing stages of development, I have found an increase in the num- 
ber of the cells composing the ectodermic wall. This is undoubtedly 
