156 THE OCEAN WORLD. 
This beautiful Porpita was discovered by Lesson on the Peruvian 
coast, where it occurred in swarms closely packed on the surface of 
the sea. “Its manner of life,” says Lesson, “is perfectly analogous 
to that of the Velella. Their locomotion on the sea is purely 
passive, at least in appearance. Their disc laid flat on the surface 
upon the water-line, leaves them to float freely and in a horizontal 
direction, the irritable arms hanging all round them.” 
MEDUSIDA. 
We here include in this family also the family Lzcernariada. 
The true Meduside were termed by E. Forbes, Cymnophthalmia, and 
the term Steganophthalmia was applied to a large section of the Lzcer- 
nariade. In the first division, according to Professor J. R. Greene, 
the umbrella-shaped organ is to be regarded as a nectocalyx, the size 
and shape of which, in relation to the polypite with which it is con- 
nected may also vary very considerably. The veil which surrounds 
the open margin of the nectosac appears never to be absent. Four 
longitudinal canals are sometimes present. From the margin depend 
tentacles, and around the margin are found the vesicles or pigment 
spots, which are supposed to be eye-spots, and being: covered by 
a prolongation of the nectocalyx. In some genera the tentacles are 
stiff, and not contractile, as is common in most of the genera. The 
reproductive organs are of the simplest kind. At a time when the 
free gonophores of the Hydrozoa had not been perfectly studied, it 
was the custom to regard these bodies as quite independent organisms, 
and they were arranged under genera and species. At last the 
singular resemblance borne by such forms to the Meduside attracted 
attention, and it was soon found that many of the Aeduside were not 
true individual organisms, but merely the reproductive buds of various 
fTydrozoa, and the conclusion was too hastily come to that the whole 
group of Medusidee ought to be abolished. The researches of J. and 
F. Miiller, Gegenbaur, and the lamented Claparade, have indicated 
the probable existence of a group of medusid forms, which appear to 
be the immediate results of true generative acts, and not of gemma- 
tion orfission. It appears safer, in the present state of our knowledge, 
to conclude—1. That several of the organisms formerly described as 
Meduside are the free gonophores of other orders of Hydrozoa. 2. 
That the homology of these free gonophores with these simple 
expansions of the body-wall which in Hydra and some other genera 
are known to be reproductive organs by their contents alone, is proved 
alike by the existence of numerous transitional forms, and an appeal 
