DEVELOPMENT OF CITRYSAORA. 357 
ruby-red tints which distinguish the birds and fishes of those 
sunny regions. ‘They are indeed of no immediate use to man, 
but their indirect services are not to be despised. They partly 
nourish the colossal whale, and thus, converted into oil, attract 
thousands of hardy seamen to the icy seas; numberless crus- 
tacea and molluscs also live upon their hosts, and are in their 
turn devoured by the mighty herring shoals, whose capture 
gives employment and wealth to whole nations of fishermen. 
Armed with that wonderful instrument, the microscope, 
naturalists have been taught to disunite in many cases animals 
which from their external resemblance were formerly supposed 
to belong to the same class or family ; and to join others to all 
appearances extremely dissimilar. Thus the Bryozoa have 
been detached from the polyps, in spite of their similitude of 
growth, while the roaming and fixed Hydrozoa have been found 
in many cases to be but alternating generations or various 
phases of development of the same animal. ‘Take, for in- 
stance, Chrysaora hysoscella (see preceding figure, page 351), 
one of our commonest jelly-fishes. The ova this free-swimming 
creature produces might naturally be supposed to develop 
Development of Chrysaora hysoscelia. 
a, Ova with gelatinous investment. band c. Free ova. d. Young Hydratuba developed theretrom. 
e. The same with eight tentacles. f. Hydratuba in its ordinary condition. g,h. More advanced 
forms, with constrictions, # A specimen undergoing fission, in which the tentacles are seen to 
arise from below the constricted portion, while its upper segments separate and become free- 
swimming zoids (x). 
themselves into equally free-swimming Chrysaore; but instead 
of this they soon become attached, and grow into a colony of 
sessile Hydratuba, as, at this stage of their career, they have 
been termed. Tor years they may thus continue, but then the 
evolutions shown in the annexed illustration take place until 
free-swimming zodids are detached, which eventually become 
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