232 BULLETIN OF THE 



kinds of individuals : the gonosonaes, which are similar to the sexual indi- 

 vidual of Velella, and the " filiform bodies," which closely resemble the cen- 

 tral polypite of Velella and Porpita. If this likeness between the parasitic 

 Hydrichthys and the free-swimming Velella is a morphological one, it may 

 throw new light on the relationship of the hydroids and Siphonophores. The 

 parasitic nature of the life of Hydrichthys leads us to compare it with the 

 strange Coelentrate organism, Polypodium hydriforme, also parasitic, described 

 by P. Owsjannikow,* and later by O. Grimm,f in the ova of Acipenser. The 

 resemblances between the two are, however, of a most distant kind, and the 

 affinities of the two are slight. 



The only stage in the life history of Polypodium which can be homologized 

 with Hydrichthys is the hydroid stage, the cylindrical hollow tube covered 

 by buds. This is the spirally twisted tube with numerous lateral append- 

 ages, figured by Ussow % in Figs. 1-5. If we suppose the hydroid of Hy- 

 drichthys to have the lateral branches reduced in size, the buds brought to 

 the side of the main axis, and the main axis itself closed at either end, flexi- 

 ble, and motile, we should have something similar to what exists in the first 

 stage of Polypodium, found in the egg of the sturgeon. I cannot, however, 

 believe that the likeness is very close between them, although the form of both 

 is undoubtedly due, in part at least, to their parasitic life on the animals with, 

 which they are associated. 



When we come to compare the organism formed from Polypodium by the 

 breaking up of or budding from the stem, and the relatively highly organized 

 Sarsia-like organism (medusa) derived from Hydrichthys, we find little like- 

 ness between them, judging from the figures of Polypodium given by Ussow, 

 and my own. I am therefore convinced that the affinities of Hydrichthys and 

 Polypodium are very remote, and that parasitism has affected them in very 

 difterent ways,§ so far as the modifications in their anatomy are concerned. 



Turris episcopalis, Fewkes. 



This beautiful medusa was found in great abundance at JNorth Head, Grand 

 Manan. The few specimens of this genus which have been found at New- 



* Arbeiten der dritten russischen Naturforscherversammlung in Kiew. Refer- 

 ence : Zeit. Wiss. Znol., XXIL 292 ; Me'langes biologiques de I'Acad. dea Sci. de 

 St. Pe'tersbourg, 1871. 



t Arbeiten der Naturforschergesellschaft zu Petersburg, 1873. 



J Morpliologisches Jahrbucb, XII. 137-153; Ann. Mag. Nat. Hist., XVIII. 110- 

 124, PI. IV. It is of course not impossible that Hydrichthys may be a transition 

 form between true hydroids like Tubularia and Syncoryne on the one hand, and 

 the extremely modified genus Polypodium on the other. The author does not 

 deny this possibility, although the relation of the two is distant. 



§ The amount of modification in tlie structure of Polypodium would naturally 

 be very much greater than in Hydrichthys, on account of its peculiar habitat 

 inside the fish. 



