31 2 
Z. ASCIDIOIDA. 
Alcyonella. 
in solution : their developement chiefly in autumn. Habitat ad 
Angliam, Linnceus. About Chelsea, Dr Shaw. Not uncommon 
in Hyde-park, and Green-park, in the centre of London, J. E. Gray. 
Near Leeds, Mr Teale. Near Howick, Northumberland, Mr E, 
Embleton. On leaves in ponds in Scotland, Sir J. G. Dalyell. 
Polypidom, when at maturity, in large amorphous compact masses, 
soft, compressible, and somewhat elastic, of a blackish green colour, 
irregularly lobulated or sinuous on the surface, which has a lubricous 
appearance, and is more or less apparently porous. The mass is com- 
posed of subcylindrical tubes rising from the base to the surface, near- 
ly parallel, connected by, or permeating, a transparent firm jelly-like 
substance, with which the tubes appear to be also partially filled. 
The tubes are simple or unbrancbed, and open outwardly by a round- 
ish or pentagonal aperture, which is closed by a thin membranous 
cover. The walls of the tubes are of the same thin membranous 
character, pellucid, colourless, or tinted with green, and without anv 
visible vessels; they contain innumerable lenticular ova of a dark 
brown colour, about half a line in their longest diameter, very hard 
and incompressible, but in drying the centre becomes depressed and 
more transparent than the edges. These singular ova are quite smooth,* 
and arranged in rows in the tubes, though not very regularly : they 
are more abundant near the surface than at the base of the polypi- 
dom, and exist in such amazing numbers as to excite surprise at the 
seeming productiveness of an animal which appears to be very partial- 
ly diffused, and is very capricious in its appearance even in ponds fa- 
vourable for its growth,- — swarming in one season, of rare occurrence 
in the next, and perhaps then for years lying dormant until some un- 
discovered cause hatches the egg and renews its pristine fertility. 
When freed from the mass, the greater number of the ova swim on 
the surface of the water, but some sink to the bottom. 
To this description, derived from specimens in a recent, but not 
living condition, sent me by Mr Embleton, I add the following par- 
ticulars derived from Mr Teale’s valuable paper. A good idea of the 
polypes will be obtained by reference to figures 5, 6, of Plate xliv, 
which are reduced copies of Raspail’s. It is organically connected 
with the mass, the tube forming its tunic, from which the animated 
body issues by a process of evolution similar to that which developes 
the horn of a snail. When developed, the head projects a short way, 
* M. Meyen says, on the contrary, that the envelope of the ovum is covered 
with very fine vibratile cilia. Bull, des Sciences Nat. xviii, 313. Has not 
Meyen mistaken the ova or seeds of the Spongilla for those of the Alcyonella ? 
for undoubtedly the ova of the latter are smooth. 
