1901) MICROSCOPICAL JOURNAL. 315 
of the valves with them. I do not know whether sucha 
tendency exists, but it is at least very probable. 
In addition to having the lateral bands very strongly 
marked, B. lilljeborgi(?) also shows the thickening along 
the back as a distinct ridge (fig. 9). That the dorsal thick- 
ening is really in the form of a sharply defined band can 
however, be also seen in B. longirostris, when views can 
be obtained either from the front (fig.3) or back (fig.2). 
There is still one other point requiring elucidation, 
namely, how is it that the ventral portions of the valves 
become detached when the shell is to form an ephippium ? 
By very careful scrutiny of a female carrying an ephip- 
pium and winter egg (figs. 4 and 8). It can be demonstrated 
that there is a line of weakness, marked by a faint doubly- 
contoured line on each valve already formed in the exact 
posftion where the anterior portion will break away. 
This line of weakness can be developed into a crack, at 
least for some portion of its length from the anterior end, 
by applying pressure. The edges of the crack are quite 
smooth. The line of weakness does not cross any of the 
EXPLANATION OF PLATE. 
Fig. 1. Ephippium of Bosmina longirostris, side view x 150; Fig. 2, 
dorsal view X 140; Fig. 3. front view (somewhat flattened out of shape), 
X I40. 
Fig. 4. Bosmina longirostris, carrying ephippium aud winter egg, x 
130. 
Fig. 5. A portion of a lateral band of chitin, with adjacent shell- 
markings (ephippium of B. longirostris), showing how the areas en- 
closed by the latter are pitted, whilst the band is structureless, x 350- 
Fig, 6. Upper portion ofa lateral band (B. longirostris), showing the 
loose pieces of chitin at its anterior end, which apparently fall away 
and produce the slit found in this position in the ephippium, x 280. 
Fig. 7. Portion of shell culture of a specimen of B. longirostris, show- 
ing probable early stage in the formation of the line of weakness be 
tween the ephippium and the ventral portions of the valves, x 180. 
Fig. 8. Bosmina lilljeborgi (?), carrying ephippium and winter egg, 
X 90. 
Fig. 9. B. lilljeborgi (?) view from above, showing the projecting 
lateral and dorsal bands of chitin, x m0. 
