20 0. E. Beecher — Origin and Significance of Spines. 



especially the pre-Devonian species. The early Sea-lilies 

 (Crinoidea), Cystideans (Cystoidea), Blastoids (Blastoidea), and 

 Star-fishes (Asteroidea) had smooth or nearly, smooth integu- 

 ments. In its early genera, even the most typically spiny class 

 of the whole sub-kingdom, the Echinoidea (Sea-urchins) had 

 very minute and insignificant spines. It is only in the late 

 Devonian and in the Carboniferous that truly spiny forms of 

 Crinoids, Star-fishes, and Sea-urchins are found. 



Of equal significance is the fact that the Echinodermata 

 together with the plants represent the most primitive type of 

 structure, one in which there is a more or less circular arrange- 

 ment of the parts or organs. The Echinodermata are the 

 highest development in this line of growth among animals. 

 They culminated in past geological ages, and from them 

 no direct line of descent can be traced (Bailey 2 and Cope 11 ). 



The conclusion from the study of the phylogenies of spinose 

 forms is parallel to the one drawn from the ontogenies ; 

 namely, that the ancestors of spinose as well as non-spinose 

 organisms were simple and inornate. 



[To be continued.] 



