348 



THE INHABITANTS OP THE SEA. 



Thus the graceful sea-fir (Sertula/ria cupressvna), the largest of 

 our native species, may attain a height of two or three feet, and 

 bear on its branches no less than 100,000 distinct microscopical 

 polypi, each with its own crown of tentacles, and each of these 

 armed with numerous thread-cells, as formidable in their way as 

 the crustacean's claw or the annelide's embrace. But though 

 each polyp has a certain share of independence yet its body is 

 continuous with the more fluid pulp that fills the branches and 

 stem of the common trunk, and by this means all the polyps of 

 it are connected together by a living thread, and made to con- 

 stitute a family whose workings are all regulated by one har- 

 monious instinct. Each of 

 these plant-like structures 

 may therefore be considered 

 as one animal furnished with 

 a multitude of armed heads 

 and mouths, and in all the 

 other compound coelenterates 

 we find a similar organisation. 

 All the soft parts of a sertu- 

 larian polypary are enclosed 

 in a horny sheath (hydro- 

 soma) which develops peculiar 

 cup-shaped processes (hydro- 

 ihecce) for the protection of 

 each individual polyp, and 

 capsules for the reproductive 

 bodies {gonoblastidia) in ■ 

 which the ova are produced. 

 The various modifications of 

 form and structure of the 

 polyps, of their hydrothecse and gonoblastidia, give rise to a 

 number of families, genera, and species. Thus in the Sertulariae 

 the polypites are sessile, biserial, alternate, or paired ; sessile and 

 uniserial in the PlumulariaB, and stalked in the Campanulariadse. 

 The free-swimming Jelly-fishes, or Acalephse, as they have 

 been named by Aristotle on account of the stinging properties 

 due to their urticating cells, are likewise among the commonest 

 objects left upon our shores by the retreating tide. When 

 stranded, they appear like gelatinous masses, disgusting to 



a. Laomedea neglecta, natural size. 



b. Portion of the lame, magnified. 



c. Reproductive body of Cmnpanutaria volutins. 

 e. Reproductive body of C. syrmga. 



