THE BRYOZOA. 



269 



Challenger Expedition" (Zoology, Vol. I.). For anatomical structure, the works of Hancock, Owen, 

 Huxley, King, and others have been consulted ; while for the habits of the animals, embryological 

 history, and systematic position of the class, Morse's various memoirs (Boston Society of Natural 

 History) have been largely quoted. To Mr. T. Davidson, F.R.S., and Professor E. S. Morse my 

 acknowledgments are due for further information kindly afforded. 



THE BRYOZOA, OR MOSS-ANIMALS. 



THIS group includes a number of usually compound organisms, often of small size, and presenting 

 remarkable varieties of form, epitomised in the English names of sea-mosses, sea-mats, sea-scurfs, and 

 lace-corals, which are applied to the most familiar examples 

 of the class. Some are erect, like, seaweeds, leafy, branch- 

 ing, and plant-like in their mode of growth ; others re- 

 semble fungi, sponges (Fig. 19, A), or simulate the delicate 

 net and lace- work of the Coral. The creeping, sub-erect, 

 and encrusting species form a distinct type, and adhere 

 to submerged rocks, shells, and stones, grow semi-para- 

 sitically on crabs, worms, or infest seaweeds, and even 

 members of their own race (Fig. 19, B). "Some," writes 

 Mr. Busk, " soft and flexible, composed wholly or in part 

 of a horny substance, form delicate growths which yield 

 gracefully to every motion of the waves, whilst others, 

 firm, rigid, and unyielding as the rocks they live upon, 

 bid defiance to the ravages of time and tempest." 



All the Moss-animals live in water, and the greater Fi S- 16. BUGULA PVRPUKOTINCTA. NATURAL SIZE. 



' . (After Hincks.) 



number or species inhabit the ocean at depths ranging 



from between tide-marks to two hundred fathoms. Some parts of the sea-bed are covered 

 with masses of their dead and living forms, and the blanched skeletons of the commoner species, 

 many of which might be mistaken for seaweeds, are among the most frequent objects cast up 

 by the retiring waves on to the shore. During life they are often very beautiful, the hard parts and 

 associated structures being transparently white, reddish-brown, and occasionally of a purple, blue, or 

 green colour. A few genera exhibit phosphorescent characters, and one (Flustra foliacea) has an 

 odour of a somewhat indeterminable nature. Nearly all occur in the form of associated growths or 

 colonies attached to foreign objects; members of one family (Selenaridce), however, are free when adult, 

 and move by means of the largely-developed projecting organs on the external surface of the colony, 

 after the fashion of some Sea-urchins. A single genus (Loxosoma) lives a solitary, independent existence, 

 attached by a foot-gland to living organisms, the buds to which it gives rise becoming detached from 

 the parent stem. In all cases the colony is founded by a free-swimming embryo, which on fixation 

 gives rise to a secondary bud, whence others rapidly develop, and thus the colony is formed by 

 a continuous process of budding or gemmation. Some parasitic species slightly alter the surface 

 of the shell they grow upon, eating away its outer surface, and reducing the shell whose shape 

 they assume to extreme tenuity. Several members of the " lip-mouthed " sub-order (Cheilostomata) 

 pierce their cellular habitations, probably by some chemical agency within the substance of the shell they 

 infest. This perforating group, represented by living forms in the Mediterranean Sea and 

 Atlantic Ocean, is known to have existed in Tertiary and Secondary epochs, and by some 

 it is inferred, during the " ancient life " period also. 



But the Moss-animals are not entirely confined to the ocean. A number of no less interesting 

 forms have become adapted for life in the fresh waters of the land. Among these, a genus dis- 

 tinguished alike for the beauty and numerical abundance of its tentacular breathing organs, whence, 

 indeed, its generic name of Cristatella* (Fig. 17) is derived, is specially remarkable as the most 

 truly active member of its class. It is, in fact, the representative among the Bryozoa of the 

 wandering genus Lingula of the Brachiopoda, and dwelling in lakes and ponds, creeps slowly 



* Latin, crista, a crest. 



