Paleontology of the Ciiicitniati Croup. 149 



MANUAL OF THK PALEONTOLOGY OF THE CIN- 

 CINNATI GROUP. 



Bv Joseph F. James, M. Sc, F. G. S. A. 

 Part IL 



(Continued from Vol. xiv, p. 72). 



CCELENTERATA. 



An extensive sub-kingdom, comprising a great variety of 

 forms in both a living and a fossil state ; widely scattered over 

 the world and found in all geological formations from the most 

 ancient to the most recent. 



It is divided by Nicholson^^ into two classes, Hvdrozoa 

 and Anthozoa, and these again are divided into sub-classes. 

 Both classes are represented by fossils in the Cincinnati group. 



The Ccelentp:rata show a considerable advance over the 

 Protozoa, there being present a simple or divided cavity, 

 which acts as an alimentary tract, and which is sometimes 

 divided into two parts. The body wall consists of two layers, 

 an "ectoderm" or outer skin, and an " endoderm " or inner 

 skin. Between these, an intermediate layer, " mesoderm," is 

 usually developed. 



Thread cells, possessed of peculiar stinging powers, are 

 present. They are provided with long lasso-like filaments, 

 that lie coiled up in the cells when at rest, but are shot out 

 rapidly when a necessity arises for their use. The tip of the 

 lasso is furnished with a number of barbs or hooks, by means 

 of which the "sting" is inflicted. A nervous system is gen- 

 erally developed. Reproductive organs are present, but a- 

 sexual reproduction, (budding or gemmation) also takes 

 place. (See Nicholson, as above, and T. Rymer Jones, "Ani- 

 mal Kingdom," 4th edition, pp. 57-59, for fuller details.) 



"Manual of Palentology, vol. i, 1SS9. pp. iyo-191. I am also indebted to this same 

 author for most of the account of the sub-divisions of this sub-kingdom, which 

 foUows. 



