272 Proceedings of the Royal Physical Society. 
tlie advent of the macula within the vesicle; and, lastly 
the formation of the enclosing membrane. 
On examining a great number of specimens of Groraia^ 
Miliolina, Potalina, and Orhulina^ I have repeatedly dis- 
covered bodies which correspond in all respects with the 
" primitive ovum'' defined above. They consist of trans- 
parent spheres or ovoids formed of a finely molecular sub- 
stance, but in which the molecules are masked or rendered 
indistinct by the highly refractive matter in which they are 
imbedded. No germinal vesicle or spot appears in the living 
specimens. It may be masked in a similar manner to the 
molecular structure ; but in a specimen of Truncatulina 
(PI. IX. fig. 6) which has been hardened in spirit, decal- 
cified by dilute nitric acid, and mounted with strong heat in 
Canada balsam, four of the segments or zooids contain each 
an ovum which shows a germinal vesicle and spot with the 
utmost distinctness, while the rest present the usual appear- 
ance of granular, low-refracting sarcode.* 
I have not been able to trace the development of the ova 
of Khizopods. Bodies similar to those I have considered 
ova in Gromia are found attached to Algae in vessels where 
that animal abounds. The ova of Gromia are very small ; 
and young Gromias slightly larger than the ova also occur. 
In Gromiay therefore, the ova may be at once transformed 
into young, and directly acquire an envelope. Such is the 
.mode of development in the ova of most of the Hydroidse, 
which are transformed into planuloid larvae without under- 
going fissure. In Orhulina, however, the ovum is of very 
large size, and consists of a colourless spherule of sarcode 
enclosed in a membraneous test and covered by a thin glairy 
layer. Here the sarcode presents traces of fissure, though 
these are lost when it is pressed out of its envelope. In both 
this genus and Truncatulina it is impossible that the full- 
sized ova can obtain exit from the animal, except by the 
destruction of the chambers of solid shell in which they are 
enclosed. In the case of Truncatulina, moreover, the ova 
are at least ten times as large as the primordial segment or 
* I shall be happy to lend this preparation to any gentleman who may take 
an interest in it. 
