352 PODOCORYNE ACULEATA. 



3. PoDOCORTNE ACULEATA, liud. Wagner, sp. 



Hydra aculeata, — Rudolph Wagner, in Iris, 1833, p. 250, pi. xi, figs. 1 — 10. 



TROPHOSOME. — 'Those hydranths which are destitute of gonophores attain- 

 ing a height of about two lines, and with usually from eight to twelve tentacles ; those 

 which, carry gonophores smaller, and with about five tentacles. 



GONOSOME. — GoNOPnoRES on short peduncles springing in an imperfect verticil 

 from the hydranth at a little distance below the tentacles ; medusa never attaining 

 complete development, having a broad, flattened summit and four stunted marginal 

 tentacles. 



General colour. — Yellowish. 



Development of Gonosome. — Observed during May. 

 Habitat. — Investing various univalve shells in the sea. 

 Batltymetrical diHirihution. — Literal zone. 

 Localiiy. — Adriatic Sea, near Trieste, Rud. Wagner. 



Towards the end of the last century Cavolini described the medusa of a Pennaria as loaded 

 with ova while still attached to the trophosome,' and though the Neapohtan zoologist failed to 

 recognise the true import of this observation, a phenomenon of vast significance in the life- 

 history of the IIydroida became thus for the first time recorded. 



From that period to the time when Rudolph Wagner discovered his Hydra acideafa no 

 further observations were made tending to show that the medusiform buds of the fixed hydroids 

 were destined to reproduce the species by the formation of fertilised ova. 



Wagner, however, saw that the medusa3 of his hydroid had, before attaining their freedom, 

 given rise to ova, which, after a time, were discharged into the surrounding water ; and though, 

 just as in the case of Cavolini's observation, the state of our knowledge of the Hyuroida at that 

 time caused the real significance of this fact to escape him, it was capable of affording to suc- 

 ceeding observers a strong argument in favour of the new views of hydroid development — views 

 which soon began to exert their influence throughout the whole study of the Hydroida. 



That the " Hydra acideata " of AVagner is a true Fodocoryne there can be little doubt. Its 

 chief difference from the Todocoryne carnea is to be found in the fact that its medusa, though 

 referable to the same type as that of the species on Avhich Sars founded his genus, appears to be 

 somewhat arrested in its development. 



Eor the description given above I have no authority beyond the original account of the 



' Cavolini, ' Mem. Polyp.,' Sprengel's translatiou, p. G5, tab. 5. 



