REPORT OX THE HYDROIDA. 
xli 
the remains of the generative mass may still throw off portions giving rise to embryos 
which become developed in a similar way into free actiniform larvae. To such larvae the 
name of Act inula may be given in order to distinguish them from the planula of other 
Hy droids. 
Development of the Egg in Myriothela . — In the development of the egg in 
Myriothela we meet with some remarkable departures from the phenomena usually 
presented in the embryonic development of the Hydroida . 1 
The eggs of Myriothela have their origin in the cells of the endodermal layer 
which forms the walls of the spadix. Certain cells of this layer in the very young 
gonophore become transformed into egg-cells which increase in number and in size 
until the cavity of the gonophore is entirely filled with them. Each egg-cell has now 
its well-defined germinal vesicle and germinal spot, and its vitelline protoplasm, but 
without any apparent vitelline membrane. 
The egg-cells continue to increase in size with the growth of the gonophore, they 
remain for some time closely pressed one against the other so as to acquire a poly- 
hedral form, but they gradually become looser, assume an oviform shape, and may 
now be easily isolated by the needle or by the mere action of the compressorium. Their 
germinal vesicle is now very large and distinct, and within the large germinal spot a 
well-defined nucleolus may be detected. 
The egg-cells have no sooner thus attained their complete separation from one 
another, and have acquired their full size in the gonophore, than they begin to present 
a very remarkable phenomenon. They lose their independent existence, and begin to 
undergo a fusion into one another ; and when the contents of the gonophore are now 
liberated by rupture of its walls under the microscope, many of these nucleated 
protoplasm masses may be seen to be united to one another by irregular pseuclopodia- 
like extensions of their substance. By the gradual shortening and thickening of these 
processes the little masses which they connect are drawn closer to one another, and 
end by becoming completely fused together into a common protoplasmic mass. In this 
mass the cell boundaries are completely lost, but numerous nucleolated nuclei may be 
seen scattered through its substance. These are almost certainly the nuclei with their 
included nucleoli of the originally independent egg-cells. 
Several such masses, eight or more, will thus be formed within the gonophore, from 
the coalesced ova. They are of an ovoid form, and do not entirely fill the cavity of 
the gonophore, while the narrow intervals between them, as well as the small space 
which separates them from the walls of the gonophore, are occupied by a substance 
which appears to consist chiefly of free nuclei and of dwindled and degraded ova, all 
apparently undergoing a process of liquefaction, and doubtless an unused residuum of 
the bodies, by the coalescence of which the compound masses had been formed. 
1 See Memoir on the Structure and Development of Myriothela, Phil. Trans., vol. clxv. pt. 2, 1875. 
(zool. CHALL. exp. — part lxx. — 1888.) Aaaa / 
