14 
Huxley on Lacinularia socialis. 
Kolliker speaks of the ova of Megalotrocha acquiring a deep 
yellow investment, as if it were a further development of those 
ova whose yolk he saw divided. I am strongly inclined to be- 
lieve, however, that he was misled by the peculiar appearance 
of the winter ova, which look as if they had undergone yolk 
division. 
Dalrymple gives a lengthened account of these peculiar ova 
in Notommata. He says that they are dark, and that their outer 
covering appears to consist of an aggregation of cells, under 
which is a second layer of cells containing pigment molecules. 
No distinct germinal vesicle, he says, is to be found in these 
ova "from the want of general transparency " (loc. cit., p. 340). 
It will be observed that all these authors consider the winter 
ova or ephippial ova and the ordinary ova to be essentially iden- 
tical^ only that the former have an outer case. The truth is, 
that they are essentially different structures. The true ova are 
single cells which have undergone a special development. The 
ephippial ova are aggregations of cells (in fact, larger or smaller 
portions — sometimes the whole — of the ovary), which become 
enveloped in a shell and simulate true ova. 
In a fully grown Lacinularia which has produced ova, the 
ovary, or a large portion of it, begins to assume a blackish tint 
(fig. 20) ; the cells with their nuclei undergo no change, but 
a deposit of strongly refracting elementary granules takes place 
in the pale connecting substance. Every transition may be 
traced from deep black portions to unaltered spots of the 
ovarium, and pressure always renders the cells with their nuclei 
visible among the granules. The investing membrane of the 
ovary becomes separated from the dark mass so as to leave a 
space, and the outer surface of the mass invests itself with a 
thick reddish membrane (fig. 21), which is tough, elastic, and 
reticulated from the presence of many minute apertures. This 
membrane is soluble in both hot nitric acid and caustic potass.* 
The nuclei and cells, or rather the clear spaces indicating them, 
are still visible upon pressure, and may be readily seen by 
bursting the outer coat. 
By degrees the ephippial ovum becomes lighter, until at last 
its colour is reddish brown, like that of the ordinary ova ; but 
its contents are now seen to be divided into two masses — hemi- 
spherical from mutual contact (fig. 22). If this body be now 
crushed, it will be found that an inner structureless membrane 
exists within the fenestrated membrane, and sends a partition 
* Leydig (1. c, p. 453) says that the shells of the ova were not dis- 
solved by maceration in a solution of caustic soda (cold ?) for twenty-four 
hours, and thence concludes that they may be composed of chitin. 
The above observation tends to the contrarj^ conchision. 
