SqUIJiTS, POL VPS, AND JELLV-FISRES. 59 



under the name of sea-fir, sea-moss, or Sertularia 

 (PI. 4, Figs. 7, 10), are, indeed, far removed from 

 plants, and even far above the 

 lowest forms of animal life. 

 To those who are acquainted 

 with the little polyp of our 

 fresh-water streams and ponds, 

 the hydra, it is but necessary 

 to say that the sea-fir is prac- polyp of sertulaeia, 

 tieally only a compound colony magniaed. 



of this animal, which has become covered over by, or 

 encased in, a horny sheath. Cast your eye over a 

 single twig of the Sertularian, and note the minute 

 scale-like bracts which run oflF at an acute angle 

 with it. These, when magnified, are seen to be 

 hollow sheaths or cups (thecse), each of which, 

 during the life of the animal, contained a minute 

 polyp, to all intents and purposes identical with 

 the hydra. The different polyps were united 

 with one another by means of a common stalk 

 which occupied the centre of the connecting axis 

 or twig. But what is the polyp itself? A hollow 

 little body, with an opening at one end, the mouth, 

 and a circle of hollow arms or tentacles, an out- 

 growth of the body-cavity itself, surrounding the 

 mouth. It might be likened to a glove closed at 

 the bottom, and with a single rupture (correspond- 

 ing to the mouth of the polyp) at the base of one 

 of the fingers. This colony has become compound 

 through repeated budding, the individual polyps 

 after they have once budded out contributing by 

 way of nourishment to the welfare qf the commu- 



