112 Wisconsin Academy of Sciences , Arts and Letters. 
are pedunculate. Undeveloped pleuropodia do not become bulbiform, 
since they never pass beyond the conical or digitiform phases common to 
all incipient insect appendages. \Neophylax .] 
6. The cells composing the pleuropodia in all cases except where these 
organs remain rudimentary or digitiform, deviate considerably in their 
structure from the ectoderm cells of the body wall and the other append¬ 
ages. The cells and nuclei increase in size and usually become more 
succulent. 
7. In most pleuropodia of the evaginate type there is a larger or smaller 
cavity, communicating by means of a narrow duct through the peduncle 
with the body cavity [ Blatta , etc.]. In the calyculate forms there is a 
second cavity, distinct from the first, opening in the opposite direction, on 
the outside of the body. 
8. No tracheae, nerves or muscles have been observed to enter into the 
formation of the pleuropodia. A few mesoderm cells, probably blood- 
corpuscles or fragments of mesenchymatous tissue, have been observed in 
the cavities of some evaginate pleuropodia. 
9. In some species the pleuropodia produce a secretion from the ends of 
their enlarged cells. This secretion may be a glairy albuminoid substance 
[ Cicada , Meloe,] a granular mass [Stenobotkrus], a bundle of threads 
[, Zaitha ], or a thick, striated, cuticula-like mass ( Acilius ). 
10. In some evaginate pleuropodia there appears a constriction, proba¬ 
bly homologous with some one of the constrictions which separate the tho¬ 
racic and maxillary appendages into metameres. 
11. In some cases, at least, no chitinous cuticle is formed over the sur¬ 
face of the pleuropodial cells. [ Blatta , Stenobothrus .] 
12. The pleuropodia attain their greatest size during the revolution of 
the embryo. Soon after the yolk has been enclosed by the body walls and 
the heart has formed, the appendages of the first abdominal segment begin 
to degenerate. 
13. The degeneration of an evaginate pleuropodium does not in all cases 
result in a reabsorption into the body of the embryo, but in a falling assun- 
der of its large cells and their subsequent dissolution outside the insect’s 
body. 
14. The pleuropodia in all their forms and stages are characterized by a 
certain incompleteness, which, together with the brevity of their existence 
even during embryonic life, stamps them as mere rudiments of what were 
probably in remote ages much larger and more complex organs. 
