No. 2.] LARVA OF CTENOPHORA ANGUSTIPENNIS. 549 
polygonal cells, which have very conspicuous nuclei. The’ 
excretory canal is clearly marked. (Fig. 22.) 
Back of the ventriculus lies the small intestine, which is of 
smaller caliber than the ventriculus. The diameter of the 
small intestine is only about one-fourth of that of the ventric- 
ulus. This opens into the fifth division of the alimentary 
canal, the large intestine. The large intestine is distinguished 
by the very large intestinal czecum or diverticulum, which is 
one of the distinguishing features of the herbivorous Tipulide. 
This cecum lies along the ventriculus and extends as far as 
the proventriculus. A somewhat similar surface is present in 
Holorusia, but it is only about one-third as large. Ona sur- 
face view the caecum appears flabby, this being due to the 
pouch-like effect produced by the transverse and longitudinal 
muscles. The walls of the diverticulum are very thin. The 
wall is composed of two layers, an outer one made up of 
annular muscles and an inner one composed of very large cells. 
(Fig. 23.) (Fig. 24.) The muscles of the diverticulum 
form a most peculiar network or muscle plexus, as it might 
be called, which in its branching and anastomosing bears a 
superficial resemblance to a nerve plexus. (Fig. 25.) There 
are eleven or more large bands of striated muscles which 
extend around the diverticulum, and these are connected by 
numerous finer cross-branches, which are also striated. (Figs. 
26 and 27.) In a few places the muscles seem to radiate 
from a central mass, but in general the ladder-like appearance 
is very marked. The striations run across both the large 
muscles and the finer connecting bands, so that the striations 
at the junctures meet at right angles. (Fig. 28.) There are 
many muscle nuclei, which, on a side view, seem to stand out 
from the fiber itself and to be surrounded by a transparent 
wall. By means of this peculiar muscle plexus, the diverticu- 
lum can be contracted in all directions at once. The gross 
structure of the plexus may best be demonstrated by mounting 
the entire wall of the caecum after first removing the inner cell 
layer by means of a very fine brush. The cellular membrane 
is also remarkable. The individual cells are very large and 
