FIG. 28. Young blastozooid of Glossophorum
sabulosum seen from its dorsal
surface. Ph.—pharynx; Ca.P.Ph.—peripharyngeal
cavities; A.D.—digestive loop;
S.N.—mediodorsal diverticulum, primordium of the nervous system; Ep.—epicardium; Ect.—ectoderm. (After J. Hjort.)
whatever group of tunicates may be considered, the bud is directly a
triploblastic sac. Upon the internal endoblastic vesicle rests all the
organogenic work, that of forming the pharynx, the peribranchial sacs,
the nervous system, the epicardium, the cardiopericardial organ, etc.
Despite such dissimilar ontogenic processes, the blastozooid is, nonetheless, identical to the oozooid (Fig. 28).
The heritage of the egg and that of the bud are thus not identical. It
is more extensive and more complex in the egg. In the bud, it is reduced
to the specific or "definitive" essentials. Ovogenic or germinal
heredity
cannot be superimposed on blastogenic or somatic heredity. Each reveals
itself by different routes, but arrives at the same end. This signifies, also,
198
PAUL BRIEN
--Ca.P.Ph.
-A.D.
>Ep.
-Ect.