'92 
Wisconsin Academy of Sciences, Arts and Letters. 
duncle but which has now broken down into a mass of cells of more or less 
irregular outline [Fig. 8 n.]. This mass of cells is augmented by the nuclei 
which are continually leaving the bulbous mass of protoplasm, and which, 
before they leave it, surround themselves with an irregular body of cyto¬ 
plasm cut from the large mass of protoplasm. This process continues while 
the whole mass of cells takes on various forms. Finally it spreads out 
between the posteriorly directed metathoracic leg and the ventral face of 
the abdomen. Fig. 9 shows a section through the remains of the pleuro- 
podium of an embryo twenty-six days old. The nuclei fail to stain more 
deeply than the protoplasm. The mass pi seems to be the remains of the 
bulbous portion marked pi in Fig. 8. In embryos a few hours older no 
traces of the organ are to be found. Its remains probably become indis¬ 
tinguishable from the granular plasmatic secretion which is found in coag¬ 
ulated masses about the legs and mouth-parts of the embryo. This granular 
plasma was originally the limpid fluid that filled the cavity of the amnion. 
It will be seen from my description that the origin, development and dis¬ 
solution of the pleuropodia is comprised within the space of fifteen days — 
from the twelfth t'o the twenty-seventh day of the whole period of de¬ 
velopment, which requires about a month. Within these fifteen days falls 
the peculiar phenomenon of revolution, which begins on the fifteenth and 
is concluded on the seventeenth day. Fig. 1 illustrates the lateral view of 
an embryo during revolution. [Sixteen days old.] The appendage [ap.] 
has reached its maximum size and already shows the constriction which 
is most marked a few days later. The amnion and serosa have ruptured 
and are passing back over the large mass of yolk. The serosa, s, with its 
large flat nuclei is contracting away from the ventral and posterior por¬ 
tions of the yolk. The amnion, a, with its much smaller nuclei still covers 
the ventro-lateral faces of the egg in continuity with the edge of the dorsad 
growing body-wall. 
For a more complete account of the revolution of the embryo I would 
refer the reader to a former paper [’89c]. 
Periplaneta orient alls . L. 
(Plate II, Fig. 10.) 
So great has been the difficulty encountered in removing the large eggs 
of this Blattid from the thick-walled ootheca in which they are deposited, 
that I have succeeded in securing only a few advanced embryos. 
As would be expected from the close systematic affinities of the insects, 
the pear-shaped pleuropodia are similar to those of Blatta , though they are 
somewhat more truncated at their ends and attached by much shorter and 
broader peduncles than in the species dealt with above. Fig. 10 represents 
a longitudinal section through one of these appendages as it appears in a 
cross section through the middle of the first abdominal segment. The 
