T etraplatia — Hand 
343 
3; that is, with the third bifurcation of the 
core of the lappet being wider on the outer 
than the inner side and with this lobe divided 
into two equal parts at its very tip. These 
lappets thus have ten terminal velar lobes. 
The fully extended lappets of three othe- 
specimens possessed unequal third bifurcar 
tions, but did not show the terminal division 
of the outermost lobe. The sizes of the spec- 
imens (3.2, 4.8, 5.0 mm.) which possessed 
ten velar projections were not significantly 
different from those which possessed only 
eight (2.4, 5.0, 5.2 mm.), and although one 
could easily assume that this variation in 
numbers of velar lobes is an age-correlated 
phenomenon it is not demonstrable as such 
from the data at hand. Attempts to determine 
the number of terminal velar lobes present on 
very small specimens (1 to 2 mm.) met with 
very desultory results. Most of these little 
animals possessed very tightly rolled lappets, 
and unrolling them is nearly impossible. On 
two specimens, however, it was possible to 
count eight terminal lobes on at least one 
lappet of each. The appearance of the division 
of the lateral terminal lobes, changing the 
number from eight to ten, may well be one 
which occurs fairly late in the development 
of these animals or may be a character which 
expresses itself in varying degrees. 
DISCUSSION 
Since Komai (1939) has so strongly es- 
poused the contention that Tetraplatia is a 
scyphozoan, considerable thought has been 
applied to test the basis for his conclusions. 
Komai has used the "octamerous arrange- 
ment of organs” and the "entodermal origin 
of the gonad” as features of a scyphozoan 
nature and has compared the lappets to the 
arms of stauromedusans. He makes a special 
point of identifying the structures usually con- 
sidered as the velum with the tentacles of the 
Stauromedusae and he points out that Tetra- 
platia also resembles the cubomedusans in 
its quadratic structure. Komai (1939, p. 248) 
finally concluded that ”... Tetraplatia is a 
primitive scyphozoon, retaining many char- 
acters of the actinula stage” and that ”... the 
fins are probably a homologue of the marginal 
lappets of the ephyra, though more highly 
differentiated.” Komai lists five lines of evi- 
dence which have been used by others to point 
to the hydrozoan nature of Tetraplatia. These 
lines are as follows: 1. the resemblance of the 
sense-organ to that of the trachymedusae; 
2. the ectodermal gonads; 3. the presence of 
a velum; 4. the absence of septa and gastral 
filaments; 5. the absence of cells in the meso- 
glea. Komai agrees that the sense-organ is 
hydrozoan in nature and says (p. 245) that 
”... this may be the most questionable point 
of the scyphozoon theory.” He states that 
items 2 and 3 above are "based on erroneous 
observations” and that 4 and 5 "are largely 
larval features.” I cannot agree with Komai’s 
conclusions and I feel that he himself has 
made some erroneous observations and inter- 
pretations. 
The sense organ (statocyst) of Tetraplatia 
clearly is hydrozoan in nature; this Komai 
readily admits although he refers to the litho- 
style as a rhopalium. The origin of the gonads, 
although not observed as a developmental 
phenomenon, seems from a study of histo- 
logical preparations to be clearly ectodermal. 
It is true that the gonads have invaded the 
coelenteron to the extent that they occur 
embedded in ridges of endodermal tissue but 
they can be seen to be covered with meso- 
gleal tissue which separates them from the 
endoderm. Komai illustrates the position of 
the gonads where they approach the surface 
at the margin and shows the gonadial tissue 
covered by a thin layer of ectoderm. There is 
no indication of any mesoglea between the 
gonad and ectoderm but he says that mesoglea 
is inserted between the ectoderm and gonads. 
Among the six specimens, prepared as serial 
sections which I studied, five were ripe or 
nearly ripe adults (four females, one male) 
and one was an unripe immature individual 
of undeterminable sex. In the ripe specimens 
there is a very definite indentation or "pore” 
