490 Wisconsin Academy of Sciences, Arts, and Letters . 
tudinal striation which may be restricted to this part or extend 
further into the cell. The ovoid nuclei lie in the center of the 
cells, the basal end being normally rounded, but the end towards 
the free edge of the cell often has the nuclear membrane crum¬ 
pled, giving to it the appearance of having been shrunken at 
this point by the preserving fluid. It is, however, noticeable 
that this irregularity when present is always at the same end. 
Each nucleus contains one or more nucleoli, and what is more 
noticeable, a peculiar hollow or cavity extending through it. 
(PL XXXIV, Pig. 6.) In transverse sections of the nucleus this 
appears as a large vacuole lying near its center; in longitudinal 
sections it varies somewhat, often extending straight through 
the nucleus, but more frequently it was curved, and if longer 
than the nucleus, bent upon itself. Within this hollow there 
was alwaysi present a brown rod-like body lying free within the 
cavity; it extended through it or was bent upon itself and then 
longer than the nucleus. In specimens stained with haematoxy- 
lin or with the safranin, gentian and orange triple stain, it 
remained of a light brown color. The whole nucleus reminded 
one of a gland, the wall of which would be represented by the 
body of the nucleus, the lumen, the hollow central cavity, while 
the rod-like body could be compared to the mass of secretion 
which had been contracted from the wall. 
The rectum is in length nearly equal to the fifth segment of 
the abdomen; it lies ventral to the ileum and functions as an air 
bladder, being filled with air in all the fresh specimens we dis¬ 
sected. The ileum enters the rectum somlwhat posterior to its 
center, the two being sharply contrasted both in external appear¬ 
ance and microscopic structure. A section shows that the wall 
of the rectum is composed of a layer of epithelial cells external 
to which is a thin coating of connective tissue. The epithelial 
cells contain each a nucleus but very little else, some having a 
small mass of protoplasm but never enough to fill the cell. The 
wall of the rectum in preserved specimens is irregularly folded, 
having the appearance of being easily distended and enlarged 
when filled with air. 
Ranantra when free in water always rises to the surface with 
the posterior end much higher than the; head. The end of the 
respiratory tube is then at the surface of the water, its normal 
position being one in which the tip of the tube reaches the sur¬ 
face, the rest of the insect remaining submerged. It retains this 
