DR. ALLMAN ON THE ANATOMY AND PHYSIOLOGY OF CORDYLOPHORA. 379 
interior of the capsule clustering round the central axis, and described by various 
naturalists as eggs. In these so-called eggs, however, there may be detected a medu- 
soid structure quite as manifest as in the ovigerous sacs of the marine Tubulariadce ; 
each of them is in fact a fixed Medusa developing within it true ova which possess 
the germinal vesicle and germinal spot, and present the phenomenon of yelk-cleavage, 
and after a time escape as locomotive ciliated embryos. It is probable however that 
in some cases the production of spermatozoa instead of ova is the true office of these 
bodies. 
In Sertularia argentea I have found the axis developed in the interior of the cap- 
sule into a body of very obvious medusoid conformation. In this body the medusoid 
structure has experienced an advance over that of the reproductive sacs of the Tubu- 
lariadce both mouth and disc are open, and four unbranched gastro- vascular canals 
are present, but it is permanently fixed, no marginal tentacula are developed, nor 
could I observe the least motion of the disc corresponding to the systole and diastole 
of the medusoids of the Tubulariadce and the Campanularice. It is supported on a 
short stem, which springs from the bottom of the capsule, and is directly continuous 
with its stomach. In this stem the ova originate and appear to escape from it into the 
stomach of the medusoid, to be discharged from the mouth into an external delicate 
vesicle, where they are retained during subsequent stages of their development. 
If the views now taken be correct, the reproductive capsules of Cordylophora, and 
those of the marine Tubulariadce, as well as the parts immediately concerned in the 
sexual reproduction of the Sertulariadce, must be regarded as distinct zooids*, pre- 
senting a more or less degraded type of medusoid structure-f'. 
On investigations into the embryology of the lower polypes, an important influence 
was exercised by Ehrenberg’s determination of the signification of the ovigerous 
capsules of Campanularia and Coryne. The existence of these capsules was, as is 
well known, supposed by the celebrated Berlin micrographistij: to indicate a distinc- 
tion of sex in the polypes of a zoophyte, the ordinary terminal polypes being con- 
sidered by him as non-sexua!, while the ovigerous capsules were maintained to be 
female polypes. This view was ardently adopted by Loven§, who, observing 
* The introduction of the term zooid into the language of zoology is of verj’ recent date. This term is 
intended to indicate each of the distinct organisms which, with various degrees of independence, express when 
taken together the total result of the development of a single ovum. It is a valuable addition to our termino- 
logy, enabling us to avoid the ambiguous sense which attaches itself to the word individual when this word is 
used in its biological signification as the logical element of a species. See Huxley, observations on Salpa, 
&c., in Philosophical Transactions, 1851, and Lecture on Animal Individuality, Ann. Nat. Hist. June 1852. 
See also Caepentee, Princ. Gen. and Comp. Physiol, p. 906. 
t Our knowledge of the egg-bearing and spermatozoa-bearing bodies of Hydra is not yet sufficiently accurate 
to enable us to decide with certainty how far the reproductive organization of this animal should be included 
in the same type with that of Cordylophora and the marine hydroid zoophytes. I believe that indications of 
a medusoid type may be here also witnessed, but further observations are necessary for the complete elucidation 
of this point. 
1 Corallenthiere des Rothen Meeres. 
§ Wiegmann’s Archiv, 1837. 
