No. 2.] BLATTA AND DORYPHORA. Lvs 
amnion cells (a) are still seen just beneath the serosa, and one 
is seen right at the narrow space between the cardioblasts. The 
last steps in the process are represented in Fig. 93. The dorsal 
ectoderm has become continuous at ec¢ in the median line. The 
two cardioblasts are still in the same stage. One of the last 
amnion nuclei is passing in surrounded by a mass of granules. 
A clear idea of the revolution of the embryo Doryphora may be 
obtained from the three stages in the diagrams. 
The method of revolution just described is very similar to that 
observed by Graber (15) in Zzza. Though he did not give a 
description of the complete process, he made the important 
observation that the serosa remains unchanged till after the chite- 
nous cuticle 1s formed. 
GENERAL REMARKS. 
Dorsal Organ. 
The term “dorsal organ’’ has been applied to the peculiar 
thick lump of cells resulting from the concentration on the dor- 
sal yolk of the remains of either the amnion or serosa, or of both, 
preparatory to their sinking into the yolk and being absorbed. 
A similarity in form and position has led many investigators 
to look for an homology between the dorsal organ of insects and 
the homonymous organ of the Crustacea. 
My observations on the dorsal organ of Cymothoa have con- 
vinced me that there are fundamental differences between the 
Crustacean and Hexapod dorsal organ. First, the dorsal organ 
of this form, and probably other Isopoda, is a structure which 
persists from an early stage almost to hatching, and may persist 
throughout life in some Branchiopoda, whereas the dorsal organ 
of insects is a very transitory structure. Secondly, the dorsal 
organ of Cymothoa seems to be a secretory organ, as was deemed 
probable by Balfour (2). I have observed that the elongated 
cells which form the organ secrete a reniform sack of chitin, 
which is joined by means of a corrugated chitinous tube to the 
cuticle shed from the surface of the embryo at a very early 
stage. Nusbaum (34) has observed that the cavities of the 
dorsal organs of J7yszs are filled with a clear substance, probably 
a secretion. 
The presence of the so-called dorsal organ in insects is prob- 
