ON THE REPRODUCTIVE SYSTEM IN THE HYDRUIDA. 375 
The structures just described in Sertularia rosacea and S. tamarisca will, I 
think, enable us to explain a peculiar feature observed in S. pumila and 
probably some other species. In S. pumila the blastostyle of both male and 
female gonangia gives off from its enlarged opercular summit several more or 
less ramified cecal tubular processes (fig. 9 d), which, instead of developing 
themselves externally, are found entirely within the gonangium, where they 
hang freely from the summit of the blastostyle. Their walls are composed both 
of endoderm and ectoderm, and their cavity communicates with that of the 
blastostyle, so that the peculiar coloured corpuscles which circulate within 
the cavity of the blastostyle are freely admitted into the cecal tubes, where 
they may occasionally be seen in active motion. The tubes can be most 
satisfactorily examined in the younger gonangia. In the older ones they will 
frequently be found to have contracted adhesions to the gonangium, to haye 
become atrophied, and, finally, even to have disappeared. 
I believe that these tubes are the exact equivalents of those which in 
Sertularia tamarisca and S. rosacea are given off from the same part of the 
blastostyle, but where, instead of growing into the cavity of the gonangium, 
they are developed in an outward direction, and assist in the formation of 
the peculiar receptacle which surrounds the acrocyst in those species*. 
Among the various modifications presented by the gonosome there is 
perhaps not one more interesting than that which we meet with in Zaomedea 
Lovéni, Allm., and at least one other allied species. In this hydroid there 
are borne upon the summit of the gonangium, and altogether external to its 
cavity, certain very peculiar gonophores, which convey the impression of 
small, fixed, imperfectly developed medusz (fig. 12 9 4). It was to these 
extracapsular gonophores that Lovén long agof called attention when he 
supported and developed the doctrine, just then announced by Ehrenberg, 
of the sexuality of the Hyproma—a doctrine which, though in its mode of 
statement not absolutely correct, was yet full of significance. 
The bodies in question are nearly spherical sacs, and occur in both the 
male and female colonies. In their walls may be demonstrated an ectotheca, 
mesotheca, and endotheca. The generative elements (m) are formed within the 
endotheca, and surround a well-developed spadix. The endotheca, however, 
is generally of short duration, becoming absorbed or ruptured under the in- 
creasing volume of its contents. In the female four very distinct radiating 
canals (/) may frequently be seen ; these spring from the base of the spadix, 
and thence run in the walls of the mesotheca towards the opposite end of the 
sac. In many cases, however, I was unable to detect any trace of these 
canals, and could never find them in the maie. We should, however, be 
scarcely justified in asserting that in such cases they are altogether absent ; 
for it is quite possible that emptiness or some other peculiar condition at 
the time of observation may have caused them to escape detection—a sup- 
* It is evidently the tubes here described to which Agassiz (Nat. Hist. U. 8. vol. iv. 
p. 329. pl. xxxii. figs. 10, 10*) refers as occurring in a North American hydroid which he 
regards as identical with the Sertularia pumila of the European coasts. He views them, 
however, as simply representing the fleshy bands which may frequently be seen in the 
trophosome of the Hydroida, extending from the outer surface of the coenosare to the inner 
surface of the chitinous periderm, and which these tubes certainly resemble when they 
become more or less atrophied and adherent to the walls of the gonangium. ‘They are also 
described and figured by Lindstrém in a paper on the development of Sertularia pumila 
(Oefversigt af Kéngl. Vetenskaps-Akademiens Férhandlingar, 1855.) 
fT Lovén, Beitriige zur Kenntniss der Gattungen Campanularia und Syncoryne, Wiegm. 
Arch. 1837. Lovén names the hydroid in which he witnessed the extracapsular gonophores 
Campanularia geniculata, which is certainly a wrong determination of the species. 
