138 Wisconsin Academy of Sciences , Arts and Letters . 
EXPLANATIONS OP THE PLATES. 
PLATE 1. 
Pig. 1. Lateral view of a Blatta embryo 16 days old [during revolution] 
a, amnion; sr, serosa; lb, labrum; md, mandible; mx, x first 
maxilla; ma? 2 , second maxilla; at, antenna; p x , p 2 , _p 3 , thoracic 
limbs; ap, pleuropodium, or appendage of the first abdominal 
segment. 
Fig. 2. Longitudinal section through the metathoracic and first three 
abdominal appendages of a Blatta embryo 12 days old; p s , 
metathoracic leg; ap, ap 2 , ap 3 , first, second and third abdo¬ 
minal appendages; ms, mesodermic somite; ecd, ectoderm. 
Fig. 3. Longitudinal section through the pleuropodium of a Blatta em¬ 
bryo 14 days old; ecd, ectoderm; ms, mesoderm; v, vacuole. 
Fig. 4. Three cells from the same series of sections as Fig. 3. Zeiss horn, 
immers., A oc. II. v, vacuole; ne , plastine nucleolus. 
Fig. 5. Five nuclei from a longitudinal section of the pleuropodium of a 
Blatta embryo 20 days old; drawn with focus on the equator- 
ial plane. Magnification same as in Fig. 4. 
Fig. 6. Longitudinal section of a pleuropodium of a Blatta embryo 19 
days old. pd, peduncle; cv, cavity; cn, constriction; v, series 
of vacuoles. 
Fig. 7. Longitudinal section from a pleuropodium of a Blatta embryo 20 
days old. Reference letters same as in Fig. 6. 
Fig. 8. Longitudinal section ot a pleuropodium from a Blatta embryo 
about 25 days old. n, nuclei; pi, protoplasm. 
Fig. 9. Section through a pleuropodium of a Blatta embryo 26 days old. 
n, nuclei; pi, protoplasm. 
PLATE 2. 
Fig. 10. Longitudinal section through a pleuropodium of an embryo 
Periplaneta orientalis , in a late stage; after the closure of the 
body walls in the median dorsal line and the secretion of the 
first cuticle, ecd, ectoderm; ms, mesoderm [connective tissue]; 
pi, protoplasm issuing from the distal end of the organ; t, tips 
of pleuropodial cells; v, vacuole; x, two pleuropodial cells 
about to pass through the peduncle into the body cavity of 
the embryo. 
