70 THE SOCIAL LIFE OF ANIMALS 



ure 8). It has been much used in studies of various 

 aspects of development, particularly by the biologists 

 who gather each summer in the research laboratories 

 at Woods Hole, Massachusetts. There are several 

 reasons for its popularity. These urchins are abun- 



FiG. 8. Arbacia, the common sea-urchin of southern 

 New England, shown from the upper surface. 



dant in near-by waters and are readily mopped up by 

 the tubful. They can be kept in good condition for 

 some days in the float cages, and eggs and sperm 

 are readily procured as needed. Also the breeding 

 season of Arbacia extends through July and August, 

 which are favored months for research at the seaside. 

 For years biologists at Woods Hole have studied 

 the embryology and physiology of developing sea- 

 urchin eggs. They have built up a painstaking, 

 almost a ritualistic, technique for handling glassware, 



