ON THE GENUS LUCERNARIA. 967 
other, but the embryonic vascular system exists, it may be 
said, in the form of a subdivided conical or hemispherical 
space between the Hey gee organ and disc; the natatory 
and gelatinous portions of the umbrella afterwards grow to- 
gether along four radial tracts, so that four wide pouches are 
formed, constituting the vascular system, and which commu- 
nicate with each other only at the border. Now, in Lucer- 
naria the gastro-vascular system remains in this condition, 
whilst in the Medusa it is more and more defined as 
the connection between the natatory and gelatinous portions 
of the disc becomes more and more intimate and extensive, 
until at last they are separate only along the lines of the 
slender radial vessels and in the annular vessel, which latter, 
however, frequently disappears also. 
But notwithstanding that we are thus compelled to regard 
Lucernaria as an aborted Medusa remaining in the condition 
of a bud, still we cannot concur in the opinion, lately ex- 
pressed by Agassiz, that Lucernaria resembles most the stro- 
bila form of Medusa; for the scyphistoma, and afterwards 
the strobila, represents a polyp in which the development 
has been arrested at a much lower stage than it is in Lucer- 
naria, since in these forms no distinct natatory sac exists, 
and, consequently, also, no rudiments of a vascular system 
are apparent. 
The resemblance of Lucernaria to an undeveloped Medusa 
is also very plainly shown besides in the mode of formation of 
the gastro-vascular system, m the position of the marginal ten- 
ticles, and of the reproductive organs. The marginal tentacles 
(4) spring, as do those of many Medusz, from the edge of 
the disc, and are assembled into groups where the radial 
vessels join the circular vessel, and may be considered in 
both cases merely as pr olongations of the gastro-vascular Sys- 
tem. The bell is, commonly, deeply notched between the 
groups of tentacles, which thence appear to be placed upon 
arm-like prolongations of the bell; and in some species there 
is a marginal papilla (p) in the imterbrachial space, which, 
from its structure, must be regarded as equivalent to a ten- 
tacle. The generative organs (g) are commonly found in 
Lucernaria, as 11 many Medusze, on the wall of the radial 
vessels ; but whilst in the latter they quite cover the slender 
vessel on the side of the natatory sac (of which vessel they 
appear to represent a nodular or elongated outgrowth), in 
Lucernaria, where the radial vessels are so exceedingly broad, 
they only appear as radiating, band-like thickenings of the 
wall of the natatory sac, which develops two such generative 
bands in the space of each gastric pouch. 
