EXPLANATION OF FIGURES. 
All the figures were drawn with the aid of an Abbé camera lucida from prepara- 
tions of Fundulus heteroclitus, Linn. 
All transverse sections were taken in serial 
order from the anterior toward the posterior end of the animal, and the draw- 
ings represent the anterior faces of the sections. 
represent the dorsal faces. 
“ao, 
au. 
wUpo. 
brs. brn. 
can. med. 
cav. pier. 
cd. 
cd. sp. 
cl. en’t. tis. 
cl.-mo. vm! 
cl. mu. 
cl. pig. 
cnt. tis. 
cel. 
cp. san. 
cta. 
dt. sq. 
ec’drm. 
ec’drm.' 
en’c. 
en’drm. 
Jor. mu. 
fos. olf. 
fs. brn. 
in. 
la. 1. 
la. mu. 
la, pet. 
la. sns. ec. 
ms’ drm. 
ms’drm. ax. 
ABBREVIATIONS. 
aorta. my tm. 
auditory vesicle. nl. 
blastopore. nl.! 
gill-pouch. nl.!! 
medullary canal. nl.* 
pericardial cavity. 
chorda. nl.t 
spinal cord. nl tt 
connective-tissue cell. nl. 
intermediate cell-mass. 
muscle cell. nl. pi. bl. 
pigment cell. oc. 
connective tissue. o. In. L. 
body cavity. pin. pet. 
blood corpuscles. pli. ec’drm. 
cuticular layer of ectoderm. pil. J. 
segmental duct. pli. pet. 
ectoderm. pref. my'tm. 
ectodermic thickening. pr’nph. 
brain. pror. 
endoderm. scl’tm. 
muscle fibre. so’plu. 
nasal pit. 
gill-cleft. spl’plu. 
intestine. 
lateral plate. tb. sq. 
muscle plate. va. san. 
pectoral plate. vn. marg. 
lateral sensory layer of ec- vs. au. 
toderm. vs. au.! 
mesoderm. 
axial mesoderm, vs. K. 
us. opt. 
ms’drm. cap. head-mesoderm. 
The drawings of frontal sections 
myotome. 
nucleus. [vision. 
nucleus in process of di- 
nucleus soon after division. 
nucleus from _ protoverte- 
bra (#4). 
nucleus from lateral plate. 
nucleus of doubtful origin. 
spindle-shaped nucleus of 
the cuticular layer. 
periblast nucleus. 
eye. 
lateral line organ. 
pectoral fin. 
ectodermic fold. 
lateral fold. 
pectoral fold. 
proliferation from myotome. 
pronephros (head-kidney). 
protovertebra. 
sclerotome. 
somatopleure (somatic por- 
tion of mesoderm). 
splanchnopleure (splanch. 
nic portion of mesoderm. 
segmental tube (duct). 
blood-vessel. 
marginal vein. 
auditory vesicle. 
ectoderm from which vs. au. 
is formed. 
Kupffer’s vesicle. 
optic vesicle. 
