8 
Siphonophora Rosarum 
of this part of the alimentary canal vary in different individuals, and in 
many cases they are complicated by the contraction of the abdominal 
segments at death. In the Text Figs. 9 and 10 are represented 
diagrammatically coils which are present in every individual, but 
complications in the form of smaller supplementary coils may occur. 
Commencing at the crop, the coiled intestine inclines towards the right, 
and in doing so, curves completely round, dips down, passes beneath the 
crop, and reaches a position on the ventral surface, slightly to the left 
of the median line. From this point, it proceeds in a posterior direction 
to about the middle of the abdomen ; then, curving abruptly, returns 
forwards until the region of the crop is again reached. Here it makes 
its final curve, and rising above the last-mentioned coil, takes a direct 
course to the anus which is placed at the posterior end of the body. 
In this last coil the intestine merges into the rectum, which at first 
widens gradually, beginning to narrow again as it approaches the anus. 
The supplementary coils mentioned above usually occur where the 
alimentary canal makes its backward curves. 
The mouth is bounded by four separate structures each contributing 
towards the formation of the oral cavity. The anterior margin is 
bounded by the pointed labrum (see Plate I, Fig. 12), and the posterior 
margin is formed by a part of the labium which takes the form of a 
small under-lip, while the remainder of the labium constitutes the beak 
or proboscis. Laterally, the mouth is bounded by two down-growths 
from the sides of the head, and these fit in between the labrum and 
the small under-lip,—the whole enclosing the small oral cavity. The 
setae in their course out of the head pass through this oral cavity, and 
the labrum has a marked groove on its inner side in which they are 
lodged before they leave the head altogether to lie in the groove in the 
upper surface of the beak. 
The mouth organs of S. rosarum agree in some points with those of 
other—and in some cases more specialised—Aphides, described by 
Witlaczil (1882), Krassilstschik (1892 and 1893), Drefus (1894), etc. One 
point of difference, however, is that my investigations fail to reveal any 
definite organ which is at all comparable to the salivary pump described 
and figured by them in other genera. 
Witlaczil (1882), in his description of the mouth organs of Aphides, 
leaves several points somewhat obscure, more especially with regard to 
the number and condition of the setae. The setae of all the Hemiptera 
have attracted a great deal of attention, because there seems to be some 
doubt as to their true homology; but it is not intended in this paper to 
