4.06 E. W. MACBRIDE. 
now become applied to the lobe No. 1 of the hydroccele. The stone-canal is 
seen opening into lobe No. 2, and the perihemal rudiment 1.2 has grown out 
into a canal insinuating itself between the ectoderm and the hydroccele. 
Fics. 77 and 78.—T wo sections of a rather older larva. Fig. 77 shows that 
the right ventral and right dorsal horns (/'p'c’. and /p"'c'.) of the left 
posterior ccelom have coalesced, and that the left posterior ccelom has thus 
acquired a ring-like form. Fig. 78 shows the formation of the anus of the 
adult. 
Fie. 79.—Section parallel to the adult plane of a larva of Stage F. Shows 
the relationships of the axial sinus, oral ccelom, and water-vascular ring (wvr.), 
the last being still incomplete; also four perihemal rudiments alternating 
with the five hydroccele lobes. 
Fies. 80 and 81.—T wo sections in same plane as Fig. 79 of a larva of Stage 
G. Fig. 80 shows the axial sinus (a’.) in process of growth to form the inner 
periheemal canal. Fig. 81 shows the completion of the water-vascular ring at 
the spot marked by the asterisk between the hydroccele lobes Nos. 1 and 5; it 
also shows the trifid form of the adult cesophagus before the mouth is formed, 
and the oral ccelom opening into the left posterior ccelom. 
Fic. 82.—Similar section of older larva in which mouth is formed. The 
five interradial lobes of the ‘‘stomach” are present, the trifid shape having 
disappeared ; and the retractor muscles of these lobes are formed from remnants 
of septum between oral and left posterior celom. The distance (R) from tip 
of arm to centre of disc ‘36 millimetre. 
PLATE 23. 
Fies. 88 and 84.—Two more sections from the same series as Fig, 82. 
Fig. 83 shows the pyloric sac with its five ceca just beginning to be bifid, 
and the mutual relations of the right hydroccele and axial sinus; also the stone- 
canal opening into the latter. Fig. 84 shows the point of origin of the rectum 
and the rudiment of rectal cecum and the relation of right posterior ccelom to 
the pyloric ceca. In Fig. 83 (pr. germ. inv.) is the involution of peritoneum 
from which the primitive germ cells are formed. 
Fies. 85—94 represent sections of abnormal larve. These sections are cut 
parallel to the larval plane, except Fig. 90, which is rather oblique to that 
plane. Magnification the same as before. 
Fics. 85 and 86.—Two sections of a larva of Stage D, or slightly 
younger. rhy. Right hydroccele developed into two distinct lobes 
lined with cubical epithelium. 
Figs. 87 and 88. Two sections of a larva between Stages D and BE. 
p'c'., st'c. Pore-canal and stone-canal of right side in connection 
with normal right hydroceele, 7.4y. Their openings into this are 
in another section. 7'/y'. A second, more ventrally situated hydro- 
