ON THE REPRODUCTIVE SYSTEM IN THE HYDROIDA. 371 
summit is separated as a distinct lid, which is then either cast off at once 
(Sertularia pumila, &c.), or it remains moveably attached by one spot of its 
edge, as by a hinge, to the margin of the 
aperture thus formed in the summit of the Fig. 9. — Female gonangium 
gonangium (Sertularia operculata, Antennu- with acrocyst of Sertularia 
laria). pumila. 
The Hydroida with naked gonophores may 
be termed “ gymnogonial”*, while those in 
which the gonophores are contained in a 
gonangium may be termed “ angiogonial” }. 
In by far the greater number of cases the 
blastostyle carries numerous gonophores, 
which always increase in maturity as they 
recede from the base and approach the 
summit of the gonangium. In some cases, 
however, the blastostyle bears but a single 
gonophore ; and then.it often happens that 
the gonophore enlarges to such an extent as 
to fill nearly the entire cavity of the gonan- 
gium, the blastostyle being pushed aside out 
of the axis, and becoming often compressed 
and flattened over the gonophore, or even 
becoming partially absorbed, so as to render 
it difficult to demonstrate its existencet. 
Sometimes the cavity of the blastostyle, 
though in the very young state quite sim- 
ple, soon breaks up, from a common point 
near the base, into several distinct tubes, 
which again unite in the common cavity of 
the plug-like summit. This has been shown 
by Agassiz to be the case in his Clytia pote- 
rium, and I have myself seen it in a nearly ’ 
allied, if not identical, species from the east a, gonangium ; 3, blastostyle; ¢, 
coast of Scotland. opercular summit of blastostyle ; 
In every adelocodonic gonophore belong- 4 d, cecal offsets from the summit of 
ing to gymnogonial genera, as well as in the blastostyle ; e, gonophore after 
most of those which belong to angiogonial having Gischanped its cantante, ste 
5 : e acrocyst; f, spadix; g, proper 
genera, the generative elements are dis- sae of acrocyst; #, external gelati- 
charged directly into the surrounding water, nous investment of acrocyst ; %, ova 
in a more or less developed condition, from contained in acrocyst ; %, young ova 
_ the summit of the gonophore. In the fe- i blastostyle. 
tales of some angiogonial species, however, the ova, instead of escaping 
directly from the gonophore into the water, are retained for some time in a 
* Tupvés, naked, and yédvos. ; 
__ +t ‘Ayyetov, a vessel, and yévos. Since the present Report was laid before the Associ- 
ation, I have seen Victor Carus’s “ Classification of the Hydroida” in the ‘ Handbuch der 
_ Zoologie,’ by Peters, Carus, and Gersticker, 1863, and find that he there employs the 
terms “gymnotoka” and “skenotoka” in the same sense in which gymnogonial and 
_ angiogonial are used in the Report. 
__{ The difference presented by the gonangia, according as they contain numerous gono- 
phores or only a single one, is regarded by Gegenbaur (‘ Generationswechsel,’ p. 38) as 
of sufficient importance to induce him to distinguish the gonangia into “ polymeric ” and 
“monomeric.” I am not disposed, however, to give much weight to this difference. which 
really consists in a comparatively trivial modification of a common sia 5 
B 
