ON THE REPRODUCTIVE SYSTEM IN THE HYDROIDA. 387 
mere organs, and regards the gonophores in both instances as special female 
animals *. 
Naturalists had now not only become familiar with the presence of true 
ova in the Hyprorpa, but they saw in the portions of the colony set aside for 
their production something more than mere organs. No one, however, had 
as yet discovered any trace of spermatozoa; Ehrenberg at this time makes 
no mention of a male element, while Lovén calls the nutritive polypites 
male, and in this view of their nature falls behind Ehrenberg, who more 
truly names them sterile or sexless individuals. 
The doctrine of the sexuality of the Hyprorpa now waited only for the 
discovery of the male element in order to receive its complete development. 
This discovery was made by Ehrenberg, who, in 1838, pointed out the real 
nature of certain conical tubercles which at particular seasons are developed 
on the body of the freshwater hydra, and had been by previous observers 
regarded as a peculiar disease to which this animal was supposed to be sub- 
ject, but which were now shown by Ehrenberg + to be true spermatophorous 
capsules, while a further and important step in this direction was made by 
Krohn, who a few years afterwards announced that he had, in the Pennaria 
Cavolini, Ehren., found certain receptacles similar in form to the ovigerous 
ones long ago described by Cavolini in the same remarkable hydroid, but 
containing spermatozoa instead of ova. Similar observations were made on 
Tubularia indivisa and on Eudendrium racemosum, as well as on Aglaophenia 
pluma (Plumularia cristata) and the Sertularia misenensis of Cavolini, in all 
of which Krohn succeeded in detecting spermatozoa t. 
It is now certain that every species of hydroid gives origin to male and 
female zooids (or, in case of such meduse as may be directly developed from 
the egg, to male and female sexually generated individuals), one destined for 
the production of ova, the other for that of spermatozoa. The separation of 
the sexes in distinct generative zooids, or in distinct individuals of a sexually 
generated offspring, is thus absolute and universal among the Hyprorpa. In 
by far the greater number of cases the separation is carried even further 
than this ; for we scarcely ever meet with male and female gonophores in the 
same colony. As an almost universal rule, then, the Hyproma are dicecious ; 
in other words, every colony is unisexual§. ; 
Some few cases of a monecious condition, however, occur. This has been 
noticed by many observers in the freshwater Hydre ||, where indeed it is the 
most usual condition. I have found it also in Plumularia pinnata, which 
sometimes carries on the same stem both male and female gonophores. In 
Dicoryne conferta too there may generally be found, among the dense forest 
of stems with which the hydroid invests the surface of univalve shells, some 
stems carrying male and others female gonophores. Each stem, however, 
carries gonophores of one sex only, though it would seem that both male and 
* Tt may here be noticed that Wagner had already (Isis, 1833, § 256, tab. xi.) found me- 
dusa-like gonophores, filled with ova, in a hydroid which he names Coryne aculeata ; but, 
not being aware of the doctrine of Ehrenberg only just announced, the exact significance 
of these bodies escaped him. 
+ Mittheil. aus den Verhandl. der Gesellsch. naturf. Freunde in Berlin, 1838. 
{ Krohn, Einige Bemerkungen und Beobachtungen iiber die Geschlechtyerhiltnisse bei 
den Sertularinen, Miiller’s Archiv, Jahrg. 1843, S. 174. 
§ Krohn had already noticed that, in all the species examined by him, the male and 
female gonophores were borne on separate colonies (Joc. cit. p. 181). 
|| See especially Prof. Allen Thomson “On the co-existence of ovigerous capsules and 
spermatozoa in the same individuals of Hydra viridis,” in Proc. Roy. Soc. Edin., No. 30, 
1845-47. 
202 
