20 PALEONTOLOGY. 



specimens ; but the number of these diminishes gradually in 

 each older stratum, while the proportion of extinct forms is 

 ever on the increase. No living species more highly organized 

 than a Ehizopod is found in the secondary rocks. Eecent 

 genera extend further back in time ; indeed a few may be 

 recognised in strata of palaeozoic age, shedding a light on the 

 probable affinities and conditions of their associates. Many 

 of the smaller groups of genera, called families, disappear in 

 the secondary, and still more in the palaeozoic period, and are 

 to a limited extent replaced by groups which no longer exist. 

 But as to the larger groups of acrite organisms and of inverte- 

 brate animals, it may be affirmed that every known fossil 

 belongs to some one or other of the existing classes ; and that 

 the organic remains of the most ancient fossiliferous strata do 

 not indicate or suggest that any earlier and different group of 

 beings remains to be discovered, or has been irretrievably lost, 

 in the universal metamorphism of the oldest rocks. 



Province I.— KADI ATA* 



Sub-Province POLYPI. 



A polype is a small soft-bodied aquatic animal which 

 generally presents a cylindrical oval or oblong body, with 

 an aperture at one of its extremities surrounded by a crown 

 of radiating filaments or " tentacles." This aperture leads to 

 the digestive cavity, which, in most Polypes, is without intes- 

 tine or vent. A very large proportion of these animals has 

 organs of support called "polyparies" or corals, of various 

 form and substance, but for the most part consisting of car- 

 bonate of lime ; and, as a general rule, locomotion is lost with 



* For the characteristic organization of the provinces, classes, orders, and 

 families of Invertebrata, reference may be made to the writer's " Lectures on 

 Invertebrata, 1 ' 8vo, Longmans, 1855. 



