48 STRETHILL WRIGHT, ON BRITISH ZOOPHYTES. 
showing a germinal vesicle and spot (fig. 8). When the ova 
are sufficiently advanced for extrusion from the generative 
cavity, the investments of the sac are ruptured, the sac as- 
sumes a long, cylindrical form (fig. 9), and a most laborious 
process of parturition commences. With each pain the ecio- 
derm of the sac contracts laterally, like the bell of a Medusa, 
and at the same time the placenta (fig. 9c) is dilated by fluid 
pumped into it from the somatic cavity of the zoophyte, so 
that the ova, which are floating in a milky fluid, are forced 
against the summit of the generative sac. Meanwhile, another 
process has been going on—the external surface of the sum- 
mit of the sac has been secreting a thick cap of gelatinous 
colline (fig. 9d), which is to form a nidus for the further de- 
velopment of the ova. The contractions become still more 
violent, until the ova are confined in a mass at the dilated 
upper part of the sac; this last is ruptured, and they are then 
forced into the gelatinous cap, which still remains attached to 
the summit of the empty generative sac (fig. 10d). The ova 
now undergo imperfect fissure, and are developed into planulee 
within their nest, from which they at last escape, and, after 
swimming in the water, doubtless become fixed and converted 
into polyps. 
Atractylis arenosa, although it gives off an immense num- 
ber of young, is one of the rarest zoophytes on our coast, 
probably on account of the low viability of its planule. While 
Sertularia pumila, one of the commonest species, the young 
of which are likewise developed in a similar gelatinous nest, 
will quickly line the vessel in which it is kept with forests of 
young zoophytes, not a single planula of Atractylis arenosa, 
of the immense number that were given off by my specimen, 
ever attained the polyp stage. 
We have in this zoophyte the reappearance amongst the 
Tubulariade of a mode of gelatinous nidification which ob- 
tains in various orders of the animal kingdom—in the Pro- 
tozoa, the Mollusca, the Annelide, the Insecta, and even 
amongst the Vertebrata, as in the common frog. We may 
ask, how is it that the ova of Hydractinia and Coryne are 
discharged into the water to float about without any protec- 
tion, while those of Atractylis arenosa, the Sertularias and 
Laomedeas, require such various provisions for their further 
development? But we do not find anything in the physiology 
of these zoophytes to answer the question. 
3. Atractylis miniata, T. 8. W. (New species.) Communi- 
cated to the Roy. Phys. Soc., February 26th, 1862. 
Polypary yellow, dendritic, branches given off at an acute 
