REPRODUCTIVE CYCLES 



635 



16 



14 



UJ 

 O 10 



O 8 

 < 



Z 6 

 O 



^ 4 



PISASTER 

 OCHRACEUS 

 JAN.'55 — FEB.'56 



J F 

 1955 



M 



M 



D J F 

 1956 



Fig. 2. Gonad index for the ochre starfish, Pisaster ochraceus, as cor- 

 related with the temperature at the Hopkins Marine Station and with day 

 length. The vertical lines on the gonad index graph indicate the spread in 

 the data (95% confidence limits). 



causative relationships. The temperature of laboratory animals should 

 be controlled during this period, but sea urchins do not do well in the 

 laboratory for prolonged periods of time. Experiments are under way 

 to determine whether gonad development and spawning in the starfish 

 can be controlled by temperature changes. 



Crisp (1957) has briefly reviewed the literature pertaining to the 

 effect of temperature on breeding. He notes that animals, which have 

 a wide range but are characteristically in teinperate waters, when liv- 

 ing in northern waters show a marked restriction of the breeding season 

 to the warmest months of the year. Loosanoff and Davis (1950) 

 showed that Venus arenaria could be brought into breeding condition 

 in winter by gradually raising the temperature of the water in which 

 ^ specimens are kept, provided they are supplied with adequate food. 



