4 
Siphonophora rosarum 
dorsal surface is raised into two conspicuous domes (Plate I, Fig. 1) which 
are very deeply pigmented and present a shiny appearance in a bright 
light. On the ventral surface the pigmentation takes the form of a 
shield upon which are two grooves in the chitin in the form of a cross 
(see Plate I, Fig. 2). These grooves—more particularly the one in the 
body axis—indicate the presence of invaginations of the chitin to form 
strong ridges of chitin (endosternites, or apodemes), which project from 
the ventral wall of the thorax into the thoracic cavity, and to which the 
muscles which move the limbs are attached. 
The antenna is peculiar in that the third joint has a number of 
tubercles scattered over its surface; and the sixth joint possesses the 
same curious ridges which are present in the apterous stage. These 
features will be dealt with in detail when considering the sense organs. 
It is probable that it is to these tubercles that Buckton refers when he 
states that the third joint of the antenna has a tendency to become 
ringed. 
The Wings. 
The wings of S. rosarum in this stage are, in common with most 
Aphides, large in comparison with the size of the body. The fore 
wings are much larger than the hind wings ; and when at rest, the wings 
are folded in the peculiar way which is characteristic of Aphides. 
During the process of folding, the internal edges of the wings ap¬ 
proximate, and at the same time are raised, so that the costal margins 
become ventral to them, and lie along the insect’s back. The result is 
that the fore wings form a kind of pent-house—of which their in¬ 
ternal margins form the ridge—enclosing the hind wings which are 
similarly folded. The process of folding is performed by several small 
muscles which are situated at the insertions of the wings. The wings 
are attached to the more strongly chitinized portions of the thoracic 
wall by a thin alar membrane which is a continuation of the upper and 
lower integuments of the wings. 
The Wing Muscles. 
Packard (1898), in his Text-Book of Entomology , gives an account 
of the various systems of muscles found in different types of insects; 
and taking his account as representative, the musculature of the wings 
in this stage of S. rosarum is comparatively simple. The wing muscles 
