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ZOOLOGY 



Starfish, showing regeneration of lost 

 arms. Notice that in the lowest 

 specimen the arm is just begin- 

 ning to regenerate. 



Regeneration. — It is no uncommon 

 thing to find starfish with fewer arms than 

 the normal number. In such specimens 

 small arms are frequently seen, making it 

 appear likely that, once having lost an arm, 

 it might grow again. Such is indeed the 

 case, the starfish having the ability to re- 

 generate (grow anew) lost parts. If a star- 

 fish should lose all five rays, it is possible 

 that under favorable conditions it might 

 regenerate all its lost parts and become as 

 active as ever in the destruction of shellfish. 



Development. — Besides this asexual 

 method of regeneration, the starfish repro- 

 duces sexually by means of eggs and sperms. 

 The sexes are separate. The eggs are passed 

 into the water; fertilization takes place 

 near the surface of the water, where the eggs 

 and sperms are found in great numbers 



during the breeding season (June-July in Long Island Sound). Develop- 

 ment proceeds at first as in the jellyfish, the egg segmenting to form 

 a blastula and gastrula. Development does not proceed directly into a 

 starfish, however, the animal being at first very unlike the adult. It swims 

 freely until a limy skeleton is developed. The starfish larva eventually 

 buds off a tiny star-shaped body which actually lives on the tissues of the 

 larva, eventually becoming a tiny starfish no larger than a small pin head. 

 At this stage of their existence they are foiuid on eelgrass and other salt- 



Sea urchins (Arbacia) showing mouth, tube feet, and movable spines. 



