AGASSIZ. NATURAL HISTORY OF THE UNITED STATES. 481 
sistent proboscis, and completely lines tbe outer wall. We have 
traced this metamorphosis up to the time when the head of the hydra 
had begun to form, and its tentacles were just far enough advanced 
to give it a knotted appearance, but unfortunately the specimens 
died, and we have not been able to investigate the matter any 
further.” May it not be that there is some error here, or has Pro¬ 
fessor Agassiz mistaken for medusa-buds, the bodies termed ‘proli¬ 
ferous polypes ’ (or stalks), by Allman, and by Huxley ‘gonoblastidia?’ 
The curious intermediate forms which connect these gonoblastidia with 
true digestive zooids, are now, at length, beginning to be known. But 
we much need a more detailed history of JKhizogeton , and a careful 
comparison of its characters at once with those of Dicoryne and Hy- 
dractinia. 
d. —In Hy dr actinia poly clina, we have a new species of this, per¬ 
haps, the most complex of the Hydroids proper. Like the European 
H. echinata , it grows “ upon the shells of Gasteropods, which served 
for the retreat of Hermit crabs but it also assumes a non-parasitic 
habit, for, “ subsequently, it has been discovered and collected in 
great abundance from rocks in tide-pools. In these latter habitats, 
it often covers several square feet with a rosy, velvet-like carpet, pre¬ 
senting a delicacy and vividness of tint which can hardly be described. 
The fact that it is often left by the tide, for five or six hours, in pools 
containing not more than a pailful of water, is enough to negative the 
assertion that the movable homes of Hermit-crabs are necessary to 
the welfare of the colonies of Hy dractinia which settle upon them.” 
The 4 Ophidian or Spiral Polypes ’ of Hr. Strethill Wright, # are stated 
by Professor Agassiz to be but modified forms of the ‘fertile Hydroids * 
(gonoblastidia), though he has not seen reproductive bodies upon 
them. Neither has he recognized the long isolated tentacles ( Ten¬ 
tacular Polyps), first described by the observer just mentioned; 
organs which appear to us homologous with the tentacles of Physalia , 
Velella and P or pita, arising from a laterally expanded coenosarc, and 
having no immediate connection with the bodies of the polypites. 
Beproductive buds sessile on the common base of the colony, as dis¬ 
tinguished from those which are borne by the gonoblastidia, were not 
observed. Some of the ophidian zooids were branched. The 4 sterile 
Hydroids ’ (polypites) of the male and female colonies differed ; the 
former having a much longer proboscis. 
e. —The new genus, Halo char is, is afterwards shown by Professor 
Agassiz to be identical with the previously described Corynilis of 
McCrady, a simple Hydroid, having a slender, naked, nearly cylindri¬ 
cal body, along which, in spiral order, are disposed the tentacles. 
These are 44 successively larger as we follow the stem upwards. The 
upper part sometimes becomes swollen to such an extent as to give 
the body a club-shaped outline, and in this state it reminds one of 
Coryne. Having no horny sheath, it can contract, from top to bot- 
* On Hydra,ctinia echinata. —Edinburgh New Philosophical Journal, April, 1857. 
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