OPHIURA BREVISPINA 



439 



of Toxopneustes, Ophiocoma, Asterias, etc., such a limit has 

 apparently been reached; but, in the increase in yolk con- 

 tent and size of egg, at the other extreme, there seems to be no 

 limit and the eggs of certain species contain an amount of re- 

 serve material capable of carrying the young considerably 

 beyond the stage at which metamorphosis has been completed 

 and in which the adult organization has been attained, viz: 

 Solaster. 



mm, 



.31S 

 .300 

 .275 

 250 

 225 



Ophmra 



/S 20 "25 30 35 W ¥S SO SS 60 DciyS 



Text fig. 4 Curve intended to indicate the correlation which exists between 

 yolk content and size of egg, and the duration of larval development in echino- 

 derms. 



Increase in the size of the egg, however, involves a corre- 

 sponding decrease in the number of eggs that can be produced 

 by an individual, and, when the eggs of a species become very 

 large and correspondingly few in number, a limit of egg-pro- 

 ducing capacity must finally be reached at which the extinction 

 of the species would be threatened, provided the normal rate 

 of mortality among the progeny were not also reduced. Brood- 

 ing of eggs and young by the parent has the effect of reducing 

 the mortality among offspring and it is a most interesting fact 



