ON NAUTILUS AND SOME OTHER ORGANISMS. 155 
ova of this species pass through a pronounced ameeboid stage 
(Figs. 4 and 5), subsequently becoming roundagain. It is also 
a favorable species for observing amceboid movements of the 
polar bodies. The movements are sluggish but unmistakable, 
and sometimes the polar bodies become widely separated from 
one another (Fig. 6). 
Fig. 4. Wie, fh. 
Fic. 6. 
Fies. 4 and 5.—Ova of Stylochus cinereus before commencement of 
segmentation, to show the ameeboid phase. Zeiss, 3 c, cam. luc. 
Fic. 6.—Ovum of S. cinereus preparing for the first division, to show 
the ameeboid character of the polar bodies. Zeiss, 3 c, cam. luc. 
Stylochus arenosus laid one irregularly contoured plate 
of eggs on May 6th. The ova were arranged in distinct rows, 
each ovum surrounded by its own proper membrane, and 
measuring 9 to 10 n. 
The egg-discs of two species of Planocera, occurring like 
the above species in shallow water off Rakaiya, offer a strong 
contrast to the egg-plates of Stylochus. I am under the 
necessity of naming these, at least provisionally, on the same 
principle as the above-described species of Stylochus. 
Planocera discus (mihi) attains a length of 45°5 mm., 
with a width of 28mm. The dorsal surface is coloured with 
delicate yellowish-brown (umber) reticulated markings, on 
which are scattered black nodal spots; interspaces whitish ; 
