stoniarh is retracted hy a sitfcial set nf imisrlcs fi n" tliis i)iir- 

 posc. 



Reproduction. A kiidwlcdi^c <it llic l)r(C'clin,!4- liahits of 

 starlishcs is iicccssar\- in dcalini;- with tliciii in rrlatimi {>> the 

 oyster industry. 



In most startishes the sexes are distinct and they can not 

 be thstinguished externally. Two general types of reproduc- 

 tion may be considered : ( 1 ) The female in most cases pro- 

 duces a vast number of minute eggs which arc fertilized in the 

 water. These develop into peculiar free-swimming larxal 

 forms (bipinnaria, brachiolaria) which do not at all resemble 

 the adult starfish. These larvae swim about by means of the 

 cilia co\'ering them or they may be carried in great numbers 

 a long distance by suitable currents of water in which they 

 are found. After some days or weeks, depending upon the 

 species and the surrounding conditions, the larvae develop 

 into small starfish able to get their food in the usual manner. 

 These facts enable one to understand why oyster beds may 

 be free from young starfish and in a few days be seriously 

 infested with a host of vigorous young forms menacing the 

 entire industry in that region. 



(2) Certain species of starfishes do not produce so large 

 a number of eggs but care for those formed in certain ways 

 which prevent so large a proportion from being destroyed. 

 These eggs do not develop into free swimming larvae, but 

 are retained in clusters about the mouth. There they pass 

 through an abbreviated development into minute young star- 

 fishes. This method has been observed in several species of 

 Henricia and other genera. In Leptychaster a large dorsal 

 brood pouch is formed over the genital orifices. In this mar- 

 supium the eggs are laid, fertilized and develop, the young 

 escaping l^y a rupture of the membrane which later heals up. 



Distribution. The starfishes are widely distributed over 

 the earth at present and extended far back into geological his- 

 tory. Their number each succeeding year is approximately 

 maintained by a series of nicely adjusted checks to a vast 

 prodigality of reproduction. If these checks could be removed 

 even in part a vast plague of starfish would soon fill the seas 

 with their progeny. Some of these checks are as follows : 

 Thousands of eggs are never fertilized ; many embryos do not 

 find suitable conditions for development; many of the ciliated 

 larvae before developing a hard exoskeleton become the prey 

 of other animals, while many of the mature animals are de- 

 stroyed by animal foes, disease or unfavorable environment. 

 AVith all of these vicissitudes we observe the mai"'^':'"'^nce of 

 the race in a moving equilibrium. 



Concerning the Pacific coast starfi.^hes. \':rrill 1914, states 

 that "The Northwestern Coast of North America seems to be 



40 



