BRYOZOA. 93 



The prodigious extent of the combined and uninterniitting labours 

 of these little world-architects must be witnessed in order to be ade- 

 quately conceived or realised. They have built up a barrier-reef 

 along the shores of New Caledonia for a length of 400 miles, and 

 another which runs along the north-east coast of Australia 1000 

 miles in length. To take a small example, a single atoll may be 

 50 miles in length by 20 in breadth ; so that if the ledge of coral rock 

 forming the ring were extended in one line it would be 120 miles in 

 length. Assuming it to be a quarter of a mile in breadth, and 150 

 feet deep, here is a mound, compared with which the walls of Babylon, 

 the great wall of China, or the pyramids of Egypt, are but children's 

 toys ; and built too amidst the waves of the ocean and in defiance of 

 its storms, which sweep away the most solid works of man. The 

 geologist, in contemplating these stupendous operations, appreciates 

 the conditions and powers by which were deposited in ancient times, 

 and under other atmospheric influences than now characterise our 

 climate, those downs of chalk which give fertility to the south coast 

 and many other parts of our native island. The remains of the 

 corals in these masses, though similar in their general nature, are spe- 

 cifically distinct from the living Polypes which are now actively en- 

 gaged in forming similar fertile deposits on the undulating and half sub- 

 merged crust of the earth, washed by the Indian and Pacific Oceans. 

 Again, those masses of limestone rocks which form a large part of the 

 older secondary formations, give evidence, by their organic remains, 

 that they are likewise due to the secretions of gelatinous polypes, the 

 species of which perished before those that formed the cretaceous 

 strata were created. As the polypes of the secondary epochs have 

 been superseded by the Porites, Milleporce, Madreporce, and other 

 genera of calcareous Anthozoa of the present day, so these, in all 

 probability, are destined to give way in their turn to new forms of 

 essentially analogous Zoophytes, to which, in time to come, the same 

 great oflfice will be assigned, to clothe with fertile lime-stone future 

 rising continents. 



LECTURE VIII. 



BRYOZOA.* 



If a deeper and truer insight into the structure and vital properties 

 of the low-organised, ramified, composite, hydriform polypes, which, 



Ciliohrachiata, Farre. 



