106 Wisconsin Academy of Sciences , Arts and Letters. 
Fig. 9, plate 2, Figs. 10a, 10b, 11 and 12, plate 3] not as digitiform, but as 
small bulbous organs with spherical contour, developed from a pair of 
small mammillar prominences. At the time of the rupture of the embry¬ 
onic envelopes, they are but little larger than the terminal metameres of 
the metathoracic legs and show but little tendency as yet to move apart 
from the places where they arose in line with the metathoracic and re¬ 
maining abdominal appendages. In sections of the last stages described 
by Heider, the beginning of a differentiation of the cells may be observed 
but the pleuropodia do not attain their greatest differentiation till a later 
stage of development. Heider reserves further description for the second 
part of his monograph. 
Melolontha vulgaris, Fabr. 
In the cockchafer the pleuropodia attain a much greater size than in any 
other insect heretofore studied. We are indebted to Graber for an ex¬ 
cellent description of these remarkable organs. [’88.] 
The pleuropodia are first seen in embryos twelve days old, and do not 
reach their maximum size till the twenty-second day. They are large flat¬ 
tened sacks attached by peduncles and, when fully developed, are much 
longer than the thoracic legs and about three times as broad. Graber 
thus describes the minute structure of the full-grown pleuropodium: 
“In respect of histological structure, a feeble magnification shows that 
the condition of the abdominal appendages differs decidedly in many, if 
not in all, particulars from that of the legs. This is especially true of the 
outer, or ectodermic layer. For, while this layer in the legs, like that of 
the body wall and all the other appendages * * * * consists 
of relatively narrow cells with relatively very small [0,006 mm] nuclei and 
only sporadically inserted larger cells with large nuclei, nearly all the cells 
in the abdominal appendages, and more especially those forming the outer 
walls of these pocket-shaped organs, are of considerable size and are pro¬ 
vided with nuclei more than twice as large as those of the remaining ecto¬ 
derm, since they measure about 0,014 mm. Considering that, at the time 
when the organ was formed, the ectoderm nuclei were 0,008 mm in diame¬ 
ter, it follows that during the course of further development, the nuclei of 
the ordinary ectoderm become somewhat smaller, while those of the ecto¬ 
derm of the abdominal appendages undergo a considerable increase in size. 
This increase is most pronounced in the outer wall of the appendage; a por¬ 
tion of the inner wall, as well as the short cervical portion, or peduncle, 
formed by constriction, having typical [i. e., small] ectodermelements.” 
Within the cavity of the sacks “are found numerous cells of the same 
structure as those which occur in the body cavity and likewise in all the 
appendages. I regard it as an open question whether these elements, origi¬ 
nating as they do from an evagination of the mesoderm, become wholly 
