46 ALEXANDER AGASSIZ 



mals, partly by artificial fertilization and partly by col- 

 lecting the tiny animals with a dip net. Miiller had 

 observed the young starfishes and sea-urchins forming at 

 the lower end of the larvae, but had supposed that they 

 were thrown off by a sort of budding process common 

 in some other Radiates, leaving the larvae to maintain a 

 separate existence. Agassiz was able to show that these 

 Echinoderms first started as two separate growths on 

 the surface of the tiny water tubes on each side of the 

 stomach, called by Miiller the " Problematical Bodies," 

 and that these two growths finally enclosed the stomach 

 and absorbed the whole of the larva, none of which 

 was cast off. The eggs of such animals are excessively 

 minute, and the whole development is on so small a scale 

 that it can be watched only by the most skillful and 

 painstaking study with the microscope. 



During the course of these investigations, Agassiz 

 noticed that at least one function of the curious little 

 growths, known as pedicellarise, lying between the spines 

 of sea-urchins, is to clean the animal from impurities, 

 which they pass along from one little arm to the next 

 till the refuse drops off on the under side of the body. 

 He was also able to declare that what had been consid- 

 ered several distinct species of starfishes were in reality 

 distinct stages in the development of our common star- 

 fish; and he called attention to the fact that the embry- 

 ology of Echinoderms is greatly modified in the so-called 

 viviparous species. The publication of the results of 

 these researches, illustrated by the most delicate draw- 

 ings from his own pencil, drew the attention of the 

 scientific world to the rising young naturalist. 



It had been found by 0. F. Miiller and others that 

 some of the higher forms of marine worms, which re- 



