Pratt— Imaginal discs. 
EXPLANATION OF PLATES. 
All figures are from preparations of Melophagus ovinus L., and were made 
with the aid of a camera lucida. The mesoderm and organs derived from it 
are colored blue, the yolk yellow. 
Abbreviations. 
a. 
anterior. 
Vvag. tr. ' 
tracheal invagination. 
am. 
amniotic rudiment. 
la. g. 
germinal plate. 
an. 
anus. 
Ing. 
sucking tongue. 
bl’drm. 
blastoderm. 
mr'py. 
micropyle. 
chn. 
chorion. 
ms’drm. 
mesoderm. 
coel. 
body-cavity. 
n. m. 
median nerve. 
corns, cb. 
cerebral commissures. 
n. v. 
ventral nerve chord. 
cr. 
heart. 
nl. 
segmentation nuclei. 
eras. stmd. 
stomodeal thickening. 
nl. vt. 
yolk nuclei. 
crs. ms’drmi. 
mesodermic ridge. 
oe. 
oesophagus. 
crs. m-v. 
mid-ventral ectodermic 
of. m. 
median opening of paired 
ridge. 
cephalic disc. 
d. 
dorsal. 
or. 
mouth. 
dsc. al. 
wing disc. 
P- 
posterior. 
dsc. ce. 
paired cephalic disc. 
phy. 
pharynx. 
dsc. ce. in. 
median cephalic disc. 
pli. ca. 
tail-fold. 
dsc. gen. a. 
anterior genital disc. 
pli. ce. 
head-fold. 
dsc. gen. p- 
posterior genital disc. 
prd. 
proctodeum. 
dsc. pd. 1. 
prothoracic leg disc. 
stmd. 
stomodeum. 
dsc. pd. 2. 
mesothoracic leg disc. 
st. pr’pl. pi. 
peripheral protoplasmic 
dsc. pd. 3. 
metathoracic leg disc. 
layer. 
en'drm. 
endoderm. 
sul. m-v. 
mid-ventral groove. 
gl. sal. 
salivary glands. 
tae. ms’drm. 
mesodermic bands. 
gn. ala. 
ganglia allata. 
tb. mpg. 
Malpighian tubules. 
gn. cb. 
cerebral ganglia. 
tr. 
trachea. 
gn. f. 
ganglion frontale. 
trt. pr’pl. 
protoplasmic paths. 
gran. vt. 
yolk granules. 
V. 
ventral. 
