THE ANATOMY AND PHYSIOLOGY OF CORDYLOPHORA. 
376 DR. ALLMAN ON ^ 
GENERAL CONSIDERATIONS. 
From the description now given, it is manifest that Cordylophora (and there i- 
little doubt that we are justified in extending the generalization to all the hydroid 
zoophytes) consists essentially of two distinct membranes, enclosing a cavity which 
opens externally by one or more orifices (polype-mouths), and which is prolonged 
into the interior of a variable number of filiform processes (tentacula)^. The two 
membranes appear to be essentially secreting structures, but the products of their 
respective secretory action strikingly differ from one another; for while the cells ot 
the eododerm give origin to secondary cells which secrete a coloured granu ar su 
stance, which may be fairly assumed as representing the biliary secretion of higher 
animals, the ectodermal cells give origin to cells of a very remarkable kind, whose 
characteristic secretion is a peculiar filament, whose import and office are as yet but 
very imperfectly understood. 
In none of these zoophytes can any approach to a specialized circulatory system 
be discovered ; the function of circulation appearing to be represented merely by a 
gradual transmission of the fluids from cell to cell, depending wholly on the per- 
meability of tissue. A respiratory system is equally without any special represen- 
tative. Whatever aerating influence the surrounding water exerts must be recened 
through the entire surface of the zoophyte, though doubtless most powerfully through 
the portion not covered by the polypary. The muscular system has begun to be 
specialized, but no trace of a nervous system can yet be detected. 
The existence of an extensive system of lacunae, as described by Dujardint, in 
some marine Tubulariadce , and by Ecker^ m Hydra, where this anatomist describes 
them as constituting a network of ramified canals, has not been confirmed by my 
own researches. , , . , , . 
The true signification of the reproductive capsules of the hydroid zoophytes is a 
matter of considerable interest. On this subject much additional light will be Uirown 
by comparing the embrvological phenomena of Cordylophora with those which are 
known to oecur in the allied genera of the sea. In the marine Tuhdariadae, tvvo 
distinct kinds of bodies are developed besides the ordinary terminal polypes. Of 
these one consists in medusa-like bodies, which are generally developed at the bases 
of the tentacular, and which after a time have been seen to detach themselves from 
the supporting polype and swim freely away. The other kind of bodies met wit i ui 
these polypes are peculiar sacs, occupying a similar position to that ot the mednsoit 
The composition of the hydroid zoophytes out of two distinct membranes has been a ready pointed out br 
Huxuey (Philosophical Transactions. 1849. Part II.). who has shown that the organs of the arc n. the 
same way essentially composed of two distinct membranes. A very important aflnnty ot structure ts tnus 
established between the hydroid zoophytes and the . c. xx ^ in i 
t Ann. Sci. Nat. 3”'= ser. tome iv. 1845. 1 ^nn. des Sc. at. ser. ome , - 
5 I„ Euienirium the medasoid bodies ore situoted »t a short distance behind the term.nal polypes, and .a 
Perigonymus, Saus. they are borne upon every part of the stems and branches. 
