DEVELOPMENT OF CHRTSAOKA. 



337 



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, Ohrysaora 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 hysoscella. 



a. Ova jvith gelatinous Investment, b and c. Free ova. d. Young Hydratuba developed therefrom. 

 e. The same with eight tentacles. /. Hydratuba in its ordinary condition. g,h. More advanced 1 

 forms, with constrictions, i'. 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 ZOOlJS (A). 



themselves into equally free-swimming Chrysaorae ; but instead 

 of this they soon become attached, and grow into a colony of 

 sessile Hydratubae, as, at this stage of their career, they have 

 been termed. For years they may thus continue, but then the 

 evolutions shown in the annexed illustration take place until 

 free-swimming zooids are detached, which eventually become 



B B 



