388 
F. M. BALFOUR. 
motion is effected. These bands are often produced into 
arm-like processes. 
Cr 
Fig. 3 . — Embryo of Brachionns urceolaris, shortly before it is hatched. 
(After Salensky.) m, mouth ; ms. masticatory apparatus ; me. mesen- 
teron ; an. anus ; Id. lateral gland ; or. ovary ; t. tail, i.e. foot ; tr. 
trochd disc ; sg. supra-cesophageal ganglion. 
The alimentary canal has, typically, the form of a bent 
tube with a ventral concavity, constituted (when an anus is 
present) of three sections, viz. an oesophagus, a stomach, and 
Fig. 4. — Diagram of an Bmbryo of Pleurobranchidium. (From Lankester.) 
f. foot ; ot. otocyst ; m. mouth ; v. velum ; ng. nerve ganglion ; 
ry. residual yolk spheres ; shs. shell-gland ; i. intestine. 
a rectum. The oesophagus and rectum are epiblastic in 
origin, while the stomach is derived from the hypoblast. 
