344 NATURAL HISTORY. 



tached, at regular distances, a multitude of shorter and 

 much more slender fibres, which are coiled up in spirals 

 when the main filament contracts, and gradually spread 

 out as it lengthens. These are very similar to the small 

 hooked threads attached at intervals along a fishing-line." 



Questions. What is said of the symmetry of the Radiates? What 

 3f the structure of the Actinias ? What is the office of the chambers 

 around the stomach ? What are the type-families among the Radi- 

 ates? What is said of the locomotion of the Radiates? What of 

 their resemblance to vegetables? What of their senses and nervous 

 system ? What are their cilia ? Describe their mode of action. 

 What purposes do they effect ? What are the three classes of Radi- 

 ates ? What is the structure of the Starfish ? In what way does it 

 walk ? How does it take its prey ? What is said of the motion of 

 its arms ? What is said of the order Stellerida? What is the struc- 

 ture of the Echinus? How does it walk? What is the plan of its 

 shell, and how does it grow? Where are the Echini found, and 

 what are their habits? What is said of their masticating apparatus? 

 What is the mode of their development? What is said of two aber- 

 rant orders of Echinndcrms ? What animals constitute the second 

 class of Radiates? What are their peculiarities? What is said of 

 the Medusae ? How are they like the Actinia?, and how unlike thorn ? 

 Where are the Acalephs generally seen ? What is said of the phos- 

 phorescence of the sea ? What is said of the Beroe ? 



CHAPTER XXXV. 



RADIATES continued. 



598. WE come now to a class of Radiates including 

 animals which are, with some few exceptions, entirely 

 different from those of the classes already considered in 

 relation to locomotion. Most of the Echinoderms crawl; 

 some of them, and all the Acalephs, swim ; but the Pol- 

 ypes are, for the most part, like plants, fixed to the spot 

 where they begin life. The older botanists described 

 these animals as plants, and arranged them with sea- 

 weeds and mosses. The Sea Anemone was considered a 

 flower, and the analogous beings found in coral and mad- 



