48 
Psyche 
[March 
ous with the mesothoracic epimeron (EM), and the postalar bridge 
contains a very reduced scolopophorous organ (SO). 
In older micropterous Cryphocricos skeletal boundaries are much 
more difficult to interpret, owing to the thickening of the cuticle, the 
differential growth of some regions, and the obliteration of folds, 
making them appear as solid thickenings rather than hollow invagina- 
tions or evaginations. Comparison of older specimens (fig. 4) with 
newly-moulted ones (fig. 3) indicates that during post-ecdysial de- 
velopment several changes have occurred in the lateral and dorso- 
lateral intersegmental region of the pterothorax. The scolopophorous 
sense organ is no longer visible on the internal surface of the postalar 
bridge. The cavity of the scutellar lobe (fig. 4; SL) has been 
reduced, and the opening into the lobe (fig. 4; dotted line) is no 
longer visible. The ventral wall of the lobe merges indistinguishably 
with the fold which borders on it ventrally. In newly-moulted 
Cryphocricos this well-defined fold (fig. 3; F) marks the boundary 
of the scutellar lobe with the metanotum medially (fig. 3; cut edge) 
and with the postnotum laterally (PN). In older adults these 
boundaries have become obscured. The fold and scutellar lobe appear 
as three separate layers only posteriorly; more anteriorly they appear 
as a single, somewhat thickened layer (fig. 4). 
In addition, the anteromedial fibers of Muscle 70, which origi- 
nate on the metanotum, attach considerably more anteriorly in older 
Cryphocricos than in younger ones (figs. 3, 4; M. 70; figs. 6, 7; 
arrows). This suggests that the fold (figs. 3, 6; F) between the 
scutellar lobe and the metanotum grows anteriorly as new layers of 
endocuticle are added to the internal surface of the skeleton. One 
older specimen, in which the muscle attached at the level indicated 
by the arrow in Figure 7, was treated in potassium hydroxide so that 
the more internal layers of endocuticle could be peeled away from 
the outermost ones. Although the inner layers lacked a fold, the 
more external ones showed a definite one which lay posterior to the 
level at which the muscle fibers had originated. 
Discussion 
In these descriptions I have taken the view that Muscle 70 origi- 
nates on the metanotum in all four types of Naucoridae. In the two 
macropterous forms (figs. 1,2) its origin is separated from the meso- 
scutellar lobe by the postnotum. In micropterous Cryphocricos (figs. 
3, 4), however, a portion of the postnotum, immediately lateral to the 
