234 RITTER. 
EXPLANATION OF PLATE XV. 
Fic. 36. A much more advanced stage; shows the peculiar folding, s.é and 
s.f’., that is produced before the siphon is complete. X 210. 
Fic. 37. Shows two of the testicular vessels, ec.ves’., projecting into the body 
space, 4.s., of the developing bud. X 21o. 
Fic. 38. Shows two vessels, ec.ves., opening into the body space. X 210. 
Fics. 39-42. Relate to the origin of the pericardial vesicle. Fig. 39 shows a 
transverse section passing through the posterior portion of the animal, and at 
r.pb.s’. is seen the pouch of the right peribranchial sac (the epicardial pouch) 
from which the pericardial vesicle is produced. Fig. 39, X 210; the others, 
X 508. 
Fic. 43. Cross-section of a bud in about the same stage of development as 
the one shown in Fig. 16. The section of the gutter-like evagination, Ay.d., of 
the ganglio-hypophyseal duct, is here very distinct. X 210. 
Fics. 44-47. Four sections of a series passing from before backward of the 
ganglio-hypophyseal duct. They are almost, but not quite, at right angles to the 
long axis of the duct. Fig. 44 shows the mouth of the duct, and Fig. 47 shows 
that at its posterior end, or near the end, the duct still communicates with the 
branchial sac, ”.¢.0. 
Both the ectoderm and the cells in the body space of these sections are repro- 
duced with special care. Figs. 44, 45, and 47, X 508; Fig. 46, X 720. 
Fic. 50. Cross-section of the duct and ganglion nearly fully formed. X 508. 
Fic. 51. Cross-section of the endostyle showing a young female polycarp. 
X 210. 
Fics. 53 and 54 (Pl. XVI). Two early stages in the formation of male poly- 
carps. X 508. 
