244 HIROSHI OHSHIMA 
space probably occupied by a jelly layer. 7d = left dorsal radial canal. 
le = left enterocoele. Ip = left pedal pit. Upe = left pedicel canal. lv = 
left ventral radial canal. ma = micropyle appendage. me = mesenchyme, 
mv = mid-ventral radial canal. = germinal vesicle. p= pedal pit. 
pb = first polar body. pe = pore-canal. ps = second maturation spindle. 
pv = Polian vesicle. re=ring canal. rd = right dorsal radial canal. 
re right enterocoele. rp = right pedal pit. rpe—right pedicel canal. 
rv = right ventral radial canal. sp = sperm nucleus. sf = stomodaeum, 
sy =syneytium. ¢=primary tentacle.  ¢, = primary tentacle in left 
dorsal interradius. /, = same in mid-dorsal interradius. /, = same in right 
dorsal interradius. ¢, = same in right ventral interradius. ¢; = same in left 
ventral interradius, 
PLATE 8. 
Fig. 1.—Very young ovarian egg, fixed on August 1, 1916. x 500. 
Fig. 2.—Immature ovarian egg cut meridionally, fixed on March 27, 
1914. x 200. 
Fig. 3.—Same as seen in the breeding season, fixed on August 1, 1916, 
x 200. 
Fig. 4.—Freshly laid egg in meridional section, showing the first polar 
body and sperm nucleus. x 200. 
Fig. 5.—Longitudinal section of blastula in which mesenchyme-forma- 
tion has begun. x 150. 
Fig. 6.—Same in which invagination has begun, x 150, 
Fig. 7.—Gastrula with still straight archenteron. Longitudinal section. 
x 200. 
Fig. 8.—Gastrula, whose archenteron has begun to bend, Longitudinal 
section. x 200. 
Fig. 9.—Tip of the archenteron to show the origin of mesenchyme 
cells and free cells in the archenteron. x 500, 
Fig. 10.—Mesenchyme cells in division. x 1,000. 
Fig. 114.—Fully-formed gastrula, whose archenteron is typically 
twisted. Cross-section to show ectodermal thickening towards the 
ventral edge of the flattened archenteron. x 200. 
Fig. 118.—The ninth section below the former in the same series, 
to show the second transverse part of archenteron, x 200. 
Fig. 11c.—The fifth section below the former in the same series, to show 
the third tubular part of archenteron. x 200, 
Fig. 124.—Gastrula of the same age as the former. Dorsal view of the 
frontal section, to show the first flat and the last tubular parts of archen- 
teron. x 200. 
Fig. 128.—The seventh section dorsad from the former, to show the 
second transverse part of archenteron. x 200, 
