34 
\V. 1’. rURCELL. 
embryos of Trocbosa singoriensis both the membranes 
bear granules (i. e. the teeth), and from his figures it is clear 
that these membranes are not fused together. 
Both these authors’ accounts may very easily be reconciled 
with one another and with mine, if we assume that their 
figures represent stages in which the preparation for the first 
post-embryonic moult had already begun. Locy’s figures then 
would represent sections in which the new cuticiila of the 
dorsal \vall of the saccule had separated from the primary 
chitinous saccule and so appeared smooth, while the ventral 
cuticula would still appear dentigerous. It may happen in 
Attus floricola that the ventral w^all of the secondary 
chitinous saccule (*■'.) becomes pulled apart from the 
primary saccule (.s-.), which, adhering to the dorsal wall, 
causes it to appear as if both walls of the saccule were pro- 
vided with denticles. This, no doubt, is the explanation of 
Jaworowslci’s statement. 
The operculum of the lung-books. — It is -well known from 
the observations of Morin (’87), Kishinouye (’90) and others 
that the outer epithelium of the pulmonary appendage forms 
the operculum, which covers each lung-book after the appen- 
dage has sunk into the body. 
It will be observed from a comparison between figs. 13b 
and 17, and between figs. IGa or 1Gb and 18, that the sides, 
as well as the distal wall, of the abdominal appendage con- 
tribute to the formation of the operculum. ’Phus, in fig. 17 
the ventral portion, w'.x'., of the operculum, to 'which the 
ventral columns of the oldest saccule, .s.l., are attached, cor- 
respond to the ventral wall, w' .x'., of the appendage in fig. 13b, 
while the distal and dorsal walls, x'.y'. and y'.z'., of the latter 
correspond as nearly as pos.sibleto the portions x'.i/ .and y'.z. 
of the operculum in fig. 17 (both figures being magnified the 
same number of times). Aline {jir. ax.) through the centre of 
the area x'.y'., or, say roughly, of the entire operculum, and 
perpendicular to its surface would, 1 think, correspond 
approximately with the original axis of the appendage. 
Since the positions of the septa and the operculum remain 
