AMPHIOXUS. 395 
Fig. 219.—THE DEVELOPMENT OF AMPHIOXUS AS SEEN IN 
SECTIONS. 
Neural Groove. Neural Tube. Neural Tube. 
Notochord. 
‘OBG OTISE|qOsoT 
‘eg dIISE[qOSaTL 
Chorda. 
,Notochord. 
; Mesoblastic 
g Somite. 
w 
rst 
p=} Arch- 
a enteron. 
a ¢ 
8 § 
vo ~ 
a 3 
rat 
o 
a 
v 
Eo 
4 
Pre-oral Sacs. 
Neuropore. 
Pre-oral SSO 
Mesoblastic Sac. EY 
ee 
es 
oI 
R 
te 
= secu 
9 sean 
Collar-sac. IAA 
SS a 
S| 
: eae 
Mesoblastic pees 
Somites. 
Trunk- sacs. Neural Tube, 
picarentsay 
‘anal, 
HO : 
._, (A Through D 1-2 in Fig. 218; B through E 3-4, and C through E 5-6 in 
Fig. 218; D through F 7-8 in Fig. 218; E through H 9-10 in Fig. 219 ; and F through 
‘posterior part of Fig. 221.) : 
A shows the neural groove and developing mesoblastic sacs; B and C show 
the neural tube ; D shows the completed mesoblastic sacs; E shows the notochord 
completely formed; and F shows the formation of myotome from dorsal part of 
mesoblast and-perivisceral ccelom from ventral. (After HATSCHEK.) 
G, Longitudinal horizontal section of an Amphioxus larva. (After M‘Brip4.) 
H, Horizontal longitudinal section through advanced chordula larva of A mphi- 
oxus. (After Hatscuex.) 
M. 21 
