98 
Wisconsin Academy of Sciences , Arts and Letters. 
globular than as represented in the figure, and is often separated from the 
granular amniotic secretion by a clearly defined space, proving that one or 
both of the secretions contract under the influence of the reagents em¬ 
ployed. From the constancy of its occurrence and the manner of its adhe¬ 
rence to the outer surface of the pleuropodium, I do not hesitate to regard 
the homogeneous mass as a secretion of the pyramidal cells. It seems 
to consist of an albuminoid substance; the vacuoles which it contains may 
be artefacts. Not having examined it in fresh embryos, I was unable to 
learn anything more concerning its physical or chemical nature. 
A somewhat more advanced embryo was examined in surface view after 
'staining with Ehrlich’s haematoxvlin. The presence of the pleuropodium 
xvas distincly indicated on each pleura of the first abdominal segment near 
the insertion of the metatlioracic leg, by a clear circular area surrounded 
by a dark ring. The clear area I take to be the cluster of hyaline cell-tips; 
the appearance of a dark circle is probably due to the ectoderm cells seen 
in section at o o together with the nucleated ends of the subjacent pleuro- 
podial cells.. 
In Cicada embryos nearly ready to hatch the pleuropodia are not to be 
found. The pyramidal cells grow pale and irregular, finally fall asunder 
and are probably absorbed. The ectoderm cells at o o grow over the small 
area formerly occupied by the hyaline cell-tips to complete the pleural wall. 
Although the pleuropodia of Cicada, being invaginated thickenings of the 
ectoderm, differ considerably from the evaginated pleuropodia of the 
Orthoptera, I believe that I am justified in regarding both forms as homo- 
logues. The facts which make for this homology are the following: 
1. The pleuropodia of Cicada are of purely ectodermic origin. 
2. They appear only on the first abdominal segment. 
8. They are at first homostichous with the thoracic and cephalic ap¬ 
pendages. 
4. Their cytological structure closely resembles that of some evaginate 
pleuropodia; the shapes of the component cells with reference to the sur¬ 
face of the body being merely reversed. Compare the pleuropodia of 
Mantis Carolina. [Fig. 11.] 
5. Their greatest development is attained during the revolution of the 
embryo. 
6. They move away from the median ventral line of the embryo and 
take the same position on the pleurae as the evaginated pleuropodia of the 
Orthoptera and Coleoptera. 
7. They atrophy and disappear before the embryo hatches. 
