232 RITTER, 
EXPLANATION OF PLATE XIV. 
Fics. 26-29. A series parallel to the last, but from a more advanced bud. 
The stage of development is about midway between the buds shown in Figs. 17 
and 18. X 210. 
Fics. 30 and 31. From the posterior end of a bud nearly as far advanced as 
the one shownin Fig.19. The sections show that the branchial sac, 67.s.,is wholly 
closed off from the peribranchial sacs, 7.4.5. and /.0.s5., and Fig. 31 shows that the 
peribranchial sacs unite behind the branchial sac to form the wide atrium, az. 
X 87. 
Fic. 32. Shows the relation of the digestive tract to the peribranchial sac 
before it has become pushed into the latter. X 120. 
Fic. 33. Shows the digestive tract pushed fully into the peribranchial sac. 
X 210. 
Fic. 34. Section of the digestive tract in the practically adult condition. The 
lacteal coecum, Z.coe. (this lettering should point to the smaller of the two circular 
structures ; the lithographer has moved the letters), the lacteal system, /.s., 
and spiral fold of the intestine, pointed to by the index line, zwt¢., are seen. 
X 210. 
Fic. 35 (and 36, Pl. XV). Two sections showing stages in the development 
of a siphon. Fig. 35 shows that the siphon begins by an evagination of the 
endodermic vesicle. X 508. 

