Tetraplatia — Hand 
337 
Fig. 5. Worldwide distribution of Tetraplatia. Dots and the shaded area in the northeastern Pacific represent 
localities which have produced T. volitans. The open circle is the locality from which T. chuni was collected. 
to-width ratio of 3:1 with the very slenderest 
specimens having nearly a 5:1 ratio. 
A number of specimens (12) were stained 
with borax carmine or rose bengal and sub- 
sequently cleared. One of the very obvious 
features of specimens so handled was the 
absence of the septum in the buttresses. Ap- 
proximately at the midpoint of the buttresses 
there may be a slight thickening of the tissues, 
but in most specimens there was an open 
endodermal passageway from the oral to 
aboral coelenteron. In some of the buttresses 
this passageway seems to be closed off by 
the endodermal lining, although in six spec- 
imens which were prepared as serial sections 
no blockage was discovered. The passageway 
is not well formed, however, and consists of 
an irregular space lined by endoderm and at 
points along its course the endoderm cells 
nearly close it off. No sign whatsoever was 
seen of a mesogleal septum. Komai (1939) 
also reports the passageway as open, but 
Dantan and Carlgren, nonetheless, have re- 
ported this septum in material they have ex- 
amined. It would seem therefore that the 
buttress canals may be closed by a mesogleal 
septum, an endodermal plug or, more com- 
monly, contain an irregular endodermally 
lined canal. No special function can be as- 
signed to the buttresses and their contained 
structures other than the obvious role the 
endodermal lining must play in the nutrition 
of the animal. 
The presence of these buttresses is the 
character which most obviously separates 
Tetraplatia volitans from T. chuni which lacks 
these structures. It was therefore of great 
interest to discover that these structures are 
not constant and that on some specimens 
only two buttresses were present. Four spec- 
