Opalina. 2953 
difference in the spherules or in the protoplasm itself? If the 
refractive spherules are products of the cytoplasm then, of course 
the primary difference between the ectosarc and endosarc must lie 
in the protoplasm itself. It seems, however not unlikely that the 
endosare spherules are derived in part at least from the chromatin 
of the nucleus. On the other hand, the spherules of the ectosare 
probably are formed by the ectoplasma itself. In O. obtrigona a few 
of the smaller spherules in the ectosare are merely endosare sphe- 
rules that have wandered toward the periphery (Fig. 6, Pl. XIV). 
In other species studied, the endosarc spherules seldom, if ever, leave 
the endosarc. Even in 0. obtrigona the migrated endosare spherules 
lie in endosare-like tissue which has protruded in strands between 
the alveoles of the ectosarc. In any case one can ignore these dis- 
placed endosare spherules in inquiring as to the differences between 
endosare and ectosare. 
That the peculiar staining reactions of the ectosare are probably 
not due to the presence of the ectosarc spherules is shown by the 
fact that in the anterior end of the body, where only a few very 
small ectosare spherules are present (Fig. 1), the ectosarc stain is 
just as divergent from that of the endosarc as it is in the rest of 
the body. That the difference in staining is not due to the absence 
of endosare spherules from the ectosarc is shown by the fact that in 
O. obtrigona the ectosarc shows the same peculiar staining reactions 
as in other species, although in this species the endosarc spherules 
migrate into the ectosarc between the large alveoles, even reaching 
the sub-pellicular layer. 
Apparently we can safely emphasize two points, first that there 
is very decided structural difference between the two regions, and 
second that there is an equally marked chemical and physiological 
difference, as indicated in the staining reactions and by the divergent 
character of the refractive spherules of the respective regions.') 
One might suspect that the ectosarc spherules are excretory 
and that one of the chief functions of the ectoplasm itself is excretion, 
were there not present in the body, in several species, such a well 
developed system of excretory vacuoles. As these vacuoles lie in the 
endosare and have no discernable connection with the ectosare, we 
seem debarred from attributing any special excretory function to the 
ectosarc. We must rest for the present with the mere statement 
) Scuvsorz (1908) finds, in Pycnothrix monocystoides, that when stained by 
van Greson’s method the ectosarc is yellow, the endosarc red. 
