144 



THE NATURE BOOK 



shells which the hermit crabs use as their 

 homes. They are really very wonderful 

 and interesting little creatures, these 

 Garland Polypes, and the life-history of 

 a large number of them is very remark- 



THE PLOCAMIUM OK BRAIDED HAIR WEED. 



able. There is a minute fonn to be found 

 growing as a single polype upon the rocks 

 in the tidal pools, which is called the 

 Hydra iiiha, and looks during the winter 

 mf)nths something like a tiny urn with 

 a circlet of feelers or tentacles. As the 

 season advances the little tubular body 

 may be seen to lengthen, and to have a 

 series of waist-like constrictions. Soon 

 the portions of the body between the 

 waists become marked with eight lobes, 

 and look rather like a tiny pile of 

 saucers placed one on top of another. 

 Next some feelers grow out round the 

 edge of the bottom saucer, and then all 

 the upper saucers break off, separate, 



turn upside down, and swim away, 

 tiny, umbrella-like things, as baby Jelly- 

 fishes. All through the summer months 

 may be seen the fragile Jelly-fishes 

 moving leisurely in the sea, but with 

 the approach of autumn they 

 produce young, which settle down 

 upon the rocks and grow into 

 Hydra tiiha. 



While the little Jelly-fishes are 

 produced simply by the division 

 of the body of the Hydra tuba, 

 a purely non-sexual process of 

 reproduction, the sexes are dis- 

 tinct in the Jelly-fishes them- 

 selves, so that their offspring, 

 the Hydra tuba, is the result 

 of sexual union. This wonder- 

 ful life-history of a sexless in- 

 dividual giving rise to male 

 and female creatures, which in 

 turn reproduce the sexless form, 

 is called an alternation of gen- 

 erations, and is one of the 

 most remarkable phenomena of 

 Xatm-e. 



We have already noticed the 

 delicate tracery of the cells of 

 one of the colonies of Moss- 

 animals {Bryozoa), partially 

 covering some of our specimens 

 of the Wrack weeds, and on 

 looking over our gatherings we 

 are pretty sure to find that we 

 have picked up one or two 

 specimens consisting of hand- 

 some frond-like masses, that 

 appear as if their whole surface had 

 been most carefully and evenly pricked 

 with a pin. These are specimens of the 

 FUisira, or Sea-mat Bryozoa, and each of 

 those ])in-holes represents a tiny dwell- 

 ing, wherein once lived a little Moss- 

 animal, and when all the members of the 

 colony were alive, and each thrust out 

 its tiny feeler-clad head, then the Fhistra 

 indeed looked as if covered with a growth 

 of moss. There are many species of these 

 Moss-animals to be found along the shore 

 and in the tidal pools, some of which 

 closely resemble the Garland Polyj^e 

 colonies in a])pearance, and are well worth 

 collecting for their graceful forms alone. 

 F. Martin Duncan. 



