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POPULAR SCIENCE REVIEW. 
witnessed a shoal in the act of spawning. 66 Myriads of speci- 
mens had clustered together so closely that they formed an 
unbroken mass. . . . They were in such a deep phalanx that 
it was impossible to ascertain how far below the surface they 
extended, while those in the uppermost layer were partially 
forced out of the water by those below.” 
At this time their energies begin to fail ; the animal flowers 
begin to fade, and the autumnal gales strew them on the 
beach. Their work is accomplished ; but the cycle of new life 
and development which they have originated is already pro- 
ceeding in the neighbouring waters. 
One or two curious peculiarities of habit may be noted* 
A species has been observed which is nocturnal in its habits : 
rarely seen by day, it swarms by night at the bottom of the 
sea, and is recognised by its phosphorescent light as it moves 
rapidly about. Another ( Polyclonia frondosa) has been ob- 
served by Agassiz on the Florida reef, “ groping in the coral 
mud at the bottom of the water, where thousands upon thou- 
sands may be seen crowded together. . . . They crawl about 
like creeping animals, now and then only flapping their 
umbrella.” This custom, so different from the usual habit of 
the Medusae, may connect itself with a peculiarity in the 
structure of the mouth and oral appendages, and the absence of 
the long marginal fishing-lines which characterise the section 
of the Order to which the species belongs ( Rhizostomece )„ 
Other naturalists report that they have seen Medusae lying at 
the bottom of the sea, with the arms turned upwards, expanded 
like a flower. This, we may suppose, is their mode of resting. 
The Discophores afford some curious instances of u commen- 
salism,” that is, the association of two animals for the benefit of 
one or both of them. Van Beneden mentions a Medusa which 
has a small fish as a permanent lodger within its body. The 
fish sails out and returns at pleasure, but finds its home with 
the Discophore. The fishermen off the coast of Jutland have 
long observed that a quantity of young fishes are always found 
beneath the disc of a large Gyancea , and sheltering amongst 
its long tentacles ; they only abandon their retreat when strong 
and swift enough to protect themselves. Another Medusa 
( Pelagia ) is accompanied by a tribe of small fishes — sometimes 
as many as twenty or thirty — which swim about in the fringes 
of the oral appendages, finding there both safety from enemies 
and food. Dr. Collingwood found a small crab residing within 
the disc of a Medusa, where no doubt he had not only free 
lodgings, but a share of the crumbs that fell from his host’s 
table. M. Quoy and Gfaimard observed a pteropod or winged 
mollusc living amongst the long tentacles of a Gyancea off the 
coast of New Holland. A crowd of small crabs and fishes had 
