^^^^ ZOOGENESIS '^ 



like polyzoans, all common and familiar objects on 

 our shores. 



While not an essential as it is for all animals in- 

 habiting the land, yet power of locomotion is a useful 

 asset for the creatures of the sea. So in the sea we 

 find great numbers of swimming creatures, as whales, 

 porpoises, seals, fish, squid (fig. 45, p. 97) and various 

 other types, and numerous crawling creatures, as for 

 instance worms (fig. 85, p. 161), crabs (fig. 19, p. 47), 

 starfishes (fig. 41, p. 71) and sea-urchins (fig. 41, p. 71). 



It is important to remember that while on land all 

 animals must seek their food and hence must be 

 endowed with powers of locomotion, or must in some 

 stage be capable of transportation, the animals of the 

 sea have a choice of three different methods of secur- 

 ing food. 



Firsf, sea animals may secure their food through 

 searching for it by crawling or by swimming, in other 

 words by the use of locomotor powers. Second, they 

 may attach themselves and let the motion of the 

 water do the work of bringing food to them. Third, 

 they may simply float and drift about suspended in 

 the midst of their food supply. 



Three different ways of securing food instead of one 

 means three times as many possibilities for major vari- 

 ations in the structure of the animals involved. So 

 we are not surprised to find that in the sea there are 

 three times as many major groups of animals as are 

 found upon the land. In the relative proportion of 

 the major groups found in the sea and on the land we 

 seem to find a close agreement with the relative pos- 



