DR. ALLMAN ON THE ANATOMY AND PHYSIOLOGY OF CORDYLOPHORA. 369 
the capsule becomes suddenly prolonged into a conical projection, surrounded near 
its apex by a circle of very minute curved spicula, the capsule at the same instant 
appearing empty (fig. 6). This phenomenon seems to consist in the sudden eversion 
through one end of the capsule of a delicate sac which had previously lain invaginated 
within it, and is generally immediately followed by the projection of a long and fine 
filament from the free end of the everted sac. The structure of these thread-cells, 
and the phenomena consequent on excitement, closely resemble what we find in the 
“hastigerous organs” of Hydra. The greater minuteness however of the thread- 
cells in Cordylophora renders it much more difficult to obtain a satisfactory examina- 
tion of their structure. The thread-cells are developed in the interior of mother- 
cells (fig. 7), which are themselves secondary cells formed within the ectodermal 
cells ; but I was not able to determine how far their development devolves exclusively 
upon certain cells of the ectoderm specially devoted to this office. The ectoderm of 
the tentacula differs slightly from that of the rest of the zoophyte, in the fact of 
the thread-cells being for the most part collected into groups, which present the 
appearance of little wart-like excrescences resembling the disposition of the cor- 
responding oigans in the tentacula of Hydra. At the extremity of the tentacula 
numerous thread-cells are crowded together, but there is no approach to the capitate 
terminations which are so striking in Syncoryne, and which, among other characters, 
zoologically distinguish that genus from Cordylophora. 
{h.) Polypary . — The polypary (fig. 3 h, b) is a cylindrical tube investing the stems 
and branches of the zoophyte, and terminating just behind a short fleshy neck which 
immediately supports the polypes. On the younger branches it forms a thin, and 
almost colourless pergamentaceous investment ; but in older parts of the zoophyte it 
is of a yellowish-brown colour, and composed of numerous layers. At the origin of 
the branches from the main stem, the polypary presents a number of annular corru- 
gations. Ihe cavity of the polypary appears by no means accurately filled by the 
coenosarc, and we almost always find a considerable interval between the ectoderuj 
of the ccenosarc and the walls of the polypary; this interval is crossed transversely 
by numerous processes of the ectoderm (fig. 3 c, c). It seems, however, almost 
certain that a very delicate living membrane is in actual contact throughout with the 
inner surface of the polypary, at least in all its younger portions ; and the space 
which appears to exist between the polypary and the coenosarc is then nothing but a 
large lacuna of the ectoderm, crossed by fleshy processes, which keep up a communi- 
cation between its opposite walls. I have distinctly demonstrated the presence of 
such a membrane in Syncoryne, where I have traced the formation of the space in 
question from a simple lacuna of the ectoderm, though I have not succeeded in so 
decidedly making out these points in Cordylophora. No trace of organization can 
be detected in the polypary, which in all respects resembles a mere secretion 
deposited in layers from the ectoderm. Where the polypary terminates anteriorly, 
an exceedingly delicate transparent pellicle may be traced in continuity with it over 
3 c 2 
