158 ARTHUR WILLEY. 
an appearance of approaching fragmentation, and it is probable 
that this is a regular occurrence. Here also the polar bodies 
execute amceboid movements. 
In the case of P. discoides I found two egg-discs on 
May 27th on the same stone on which the adults were living. 
To the unaided eye they were not to be distinguished from 
those of P. discus, but microscopic examination showed 
that the gelatinous matrix! in which the egg-capsules were 
{> 
Fic. 8.—Four egg-capsules from an egg-disc of Planocera discoides 
each capsule contains four ova. Zeiss, 3 a, cam. luc. 
arranged in concentric rows was more continuous, and not 
divisible into concentrically disposed tubes; and, above all, that 
in each egg-capsule there were only four ova (Fig. 8). 
Of the four ova in each capsule, as a rule, only two develop 
into ciliated embryos; frequently, however, three, and rarely 
only one. I have in no instance found four ciliated embryos 
in a capsule. Those ova which do not develop undergo frag- 
mentation. I think the particles of the fragmented ova must 
be dissolved in the fluid contained in the capsules, and not 
absorbed by the remaining ova in the solid form. When two 
or three embryos are revolving in a capsule, there is usually no 
trace whatever of the previous existence of other ova in the 
same capsule ; and when there is only one embryo in a capsule 
it is no larger than other embryos. 
It is chiefly before the embryos begin to revolve that the 
1 A large number of amceboid bodies may be observed in the matrix in 
which the egg-capsules are embedded in this species. 
