CORYDENDRIUM PARASITICUM. 263 



Development of Gonosome. — Summer. 



Habitat. — Growing on the liydrorhizal stolons of Eudendrium racemosnm (Cavolini). 



Batkymetrical distribution. — Litoral zone ? 



LocaJitij. — Bay of Naples, Cavolini. 



Since the time when Cavolini, towards the end of the last century, described his Sertularin 

 parasitica, no one has met with this remarkable hydroid ; and though Cavolini's description of it 

 is, like all his others, full and lucid, we must wait for farther observations made with the advan- 

 tages aftbrdcd by our presc^nt knowledge of the Hydroida, in order that some points of which 

 we are as yet ignorant in its structure and habits may be cleared up. 



That it produces phancrocodonic gonophores there can be no doubt from Cavolini's descrip- 

 tion and figures, though the Neapolitan zoologist takes them for budding hydranths. It follows 

 too from his description that the main stems consist of a fascicle of tubes which breaks up into 

 single tubes before entering the branches ; and though it would seem that he believed the bundle 

 of tubes composing the stem to be enveloped in a common pcrisarc, it is more probable that each 

 tube has its own perisarcal investment as in other fascicled hydroids. 



A remarkable feature is found in the great extent to which the hypostome can be elongated 

 and dilated ; indeed, Cavolini's figure of the hypostome when thus distended reminds one of the 

 exserted proboscis of certain annelides. 



A curious fact on which Cavolini dwells at considerable length is the occurrence at certain 

 periods of egg-like bodies in the interior of the hydrocaulus where they replace the coenosarc, and 

 from which they are subsequently discharged through the extremities of the branches now 

 destitute of hydranths. 



Cavolini takes these bodies for the proper eggs of the hydroid, and even describes their 

 development into young trophosonies ; but as it is rather by inference than by direct observation 

 that he traces his young hydroids from the supposed eggs, we must here withhold assent from his 

 conclusions. Indeed, it is far more probable that the egg-like bodies are parasitical organisms 

 than that they have any direct relation with the hydroid. ^ 



Cavolini always found the present species growing from the root-like basis of the Eudendrium 

 racemosum after the hydi-anths of the Eudendrium had perished and disappeared. He accordingly 

 regards it as a parasite of the Eudendrium at whose expense he imagined it to live, and it was 

 this supposed habit which suggested to him the specific name by which he has designated it. 

 It is almost certain, however, that there is here no case of true parasitism, and it is very likely 

 that the Corydendmm parasitieum enjoys other habitats as well as that Avhich was alone known 

 to the celebrated Neapolitan observer. 



^ We may here, however, compare Cavolini's account of these egg-like bodies with an observation 

 made by F. E. Schulze on Cordyloptiora tacustris. Schulze informs us that he had occasionally met 

 witli bodies indistinguishable from young ova imbedded in the ectoderm of the branches of 

 Cordi/loptwra. (Schulze, ' Ueber Cordylophora Lacustris,' p. 37). A very similar observation had been 

 made on Hijdractinia ecJdnata by M. de Quatrefages. See above, p. 2.23. 



