232 BULLETIN OF THE 
kinds of individuals: the gonosomes, 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, Polypodiwm hydriforme, also parasitic, described 
by P. Owsjannikow,* and later by O. Grimm, 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 tf 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 North 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. Zool., XXII. 292; Mélanges biologiques de l’Acad. des Sci. de 
St. Pétersbourg, 1871. 
+ Arbeiten der Naturforschergesellschaft zu Petersburg, 1878. 
t Morphologisches Jahrbuch, XII. 137-153; Ann. Mag. Nat. Hist., X VIII. 110- 
124, Pl. 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 the structure of Polypodium would naturally 
be very much greater than in Hydrichthys, on account of its peculiar habitat 
inside the fish. 
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