24 



INVEETEBEATA 



CHAP. 



produced, and those variations are preserved which adapt the 

 organism at the right time to the new mode of life. 



A 



cir- 



FIG. 9. The stalked larva and adult form of Antedon multispina. (After P. H. Carpenter.) 



A, larva. B, adult. 7j, Basal plate ; cir, cirrus ; pin, pinnule ; ?-i, first radial plate ; 

 r2, second radial plate ; r*, third radial plate. 



If, then, the last stages in developmental history are, so to speak, 



