866 PENNARIA GIBBOSA. 



and mamiljrium, tlioiigli lie overlooked their relation to free medusa;, and thus failed to recog- 

 nise the importance of an observation which nearly half a centiuy later became an essential 

 element in all true conceptions of hydroid morphology. 



The filiform tentacles are very remarkable in the possession of blunt swollen extremities. 

 This condition did not escape Cavolini, who has represented it in his figure, and it was very 

 distinct in Professor Trinchesi's specimen. It is plainly a persistent feature indicating an 

 approach to true capitate terminations, and must not be confounded with the temporary enlarge- 

 ment frequently noticed in other hydroids as the result of certain states of contraction. It is here, 

 on the contrary, connected with a difference of structure, the enlarged e.xtremity being loaded 

 with minute thread-cells as in a true capitulum. A very similar condition is presented by the 

 proximal circlet of tentacles in the Actinulaj of TiihuJaria. 



The body of the hydranlh is borne on a little disc, which intervenes between it and the 

 summit of the supporting ramulus, whose diameter the disc but slightly surpasses. 



Though the gonophores of Pennaria Cavolinii are truly phanerocodonic, it is probable that 

 they never become free. Those described by Cavolini were female, and were seen to be loaded 

 with ova while still attached to the trophosome, and the same was the case in the specimen 

 examined by myself. The codonostome is very much contracted, and the ova appear to be 

 retained within the cavity of the umbrella for some time after their escape from the walls of 

 the manubrium. Indeed, it would seem from Cavolini's figure that they undergo their change 

 into planuke before liberation from the medusa. The male gonophore has since been described 

 by Kolliker,^ from specimens obtained at Messina. According to him, the codonostome in these 

 is like that of the female provided with marginal tentacles in the form of four short lobes. No 

 notice is taken of these processes by Cavolini ; they were, however, very evident in Prof. 

 Trinchesi's specimen, which, like that figured by Cavolini, was a female, and there is little doubt 

 that the rudimental tentacles have been overlooked by the Neapolitan zoologist. 



*^* 3. Penxaki.a. GIBBOSA, Agassiz. 



Pennaria gibbosa, — Agassiz, Contr. Nat. Hist. U.S., vol. iii, pi. xv, figs. 1 and 2, and vol. iv, 

 p. 378. 



TROPHOSOME. — Hydkocaultjs attaining a height of at least four inches ; main 

 stem slightly zig-zag, and with a long and gentle curve from its base to its summit, 

 branches given off alternately at regidar intervals from each side with a distichous 

 arrangement ; main stem annulated at its base, and with a few annulations in each 

 interval between the branches ; primary branches annulated at their base and summit, 

 and with a few annulations at the distal side of the point of origin of each ultimate 

 ramulus. Hybrantus borne on the summits of very short ultimate ramuli, and on 



1 'Zeltsclu-. f. Wiss. Zool.,' 1853, p. 303. 



