THE INVERTEBRATES 143 



young sea-urchins are free swimming creatures of very 

 different appearance from the adults. Their food consists 

 of small marine animals and of bits of organic matter which 

 they collect from the sand and debris of the ocean floor. 

 Many of the sea-urchins are gregarious, living together in 

 great numbers. Some have the habit of boring into the 

 rocks of the shore between tide-lines. I have seen thousands 

 of small, beautifully colored purple sea-urchins lying each in a 

 spherical pit or hole in hard conglomerate rock on the 

 California coast. How they are enabled to bore these 

 holes is not yet known. There is great variety in size and 

 color among these animals. The colors are brown, olive, 

 purple red, greenish blue, etc. 



A few kinds of sea-urchins have a flexible shell or test. 

 The Challenger expedition dredged up from the sea bottom 

 some sea-urchins, and when placed on the ship's deck 

 "the test moved and shrank from touch when handled, and 

 felt like a starfish." The cake-urchins or sand-dollars are 

 sea-urchins having a very flat body with short spines. They 

 lie buried in the sand, and are often very brightly colored. 

 Their hard bleached tests with the spines all rubbed off 

 are common on the sands of both the Atlantic and Pacific 

 coasts. 



Worms. — ^In the older classifications the branch Vermes 

 included all the animals which are now divided into 

 four branches of terrible names (Platyhelminthes, Nema- 

 thelminthes, Trochelminthes and Annulata). Vermes were 

 worms; that was easy to remember. But with the discovery 

 of many new worm-like creatures and of new things about 

 some of the old ones called worms naturalists have decided 

 that the old easy grouping was not a correct one. Hence 

 the new one. 



Bring into the schoolroom large live earthworms. They 

 may be found in the daytime by digging, or at night by 

 searching with a lantern. They often come above ground 



