50 BASIC METHODS FOR EXPERIMENTS 



after at 30 second intervals to dishes containing 250 cc. of sea- 

 water. In this wise, the optimum exposure for development 

 to the pluteus stage is determined. 



Increase in temperature 



Increase in temperature has been used for the experimental 

 initiation of development, especially by R. S. Lillie on the 

 starfish egg. AUyn has used it on the egg of Chaetopterus. 

 According to her, this is the only means which gives develop- 

 ment with cleavage in this egg. I have used elevation of tem- 

 perature on the egg of Nereis and have found that it gives a 

 development (with cleavage) which is scarcely to be distinguished 

 from the normal. For the egg of Nereis, increase in temperature 

 may be employed in two ways. 



1. On the evening of capture, or at latest the morning after, 

 females having been carefully washed in gently running sea- 

 water are rapidly dried on soft filter paper and placed in tubes 

 containing sea-water at temperatures of 30, 31, 32 and 33°C. 

 The females should shed the eggs at once. The eggs extrude the 

 jelly immediately thereafter. At 5 minute intervals, pipette a 

 drop of eggs to finger bowls containing sea-water at room tem- 

 perature (18 to 20°C.). The effective exposure gives more than 

 90 per cent, trochophores. 



In this method, it is important that the eggs come into the 

 warm sea-water without having been in sea-water of lower tem- 

 perature. If, for example, the eggs are washed in sea-water by 

 removing them from the female to sea-water at room tempera- 

 ture, they will not respond to warm sea-water, although they 

 have suffered no diminution in fertilization-capacity. If the 

 eggs are shed during the process of drying the female, they may 

 be successfully exposed to the warm sea-water. However, it is 

 best not to cut the female in order to obtain the eggs, for thus 

 blood introduced with the eggs into the warm sea-water lowers 

 the quality and per cent, of the response. (Just, 191 5.) 



2. I have used also the method of exposing the eggs to higher 

 temperature for about 60 seconds. In this method, the eggs may 

 be removed from sea-water at room temperature to sea-water 

 warmed to 40°C. But the response of the eggs is not as good 

 as in the case of eggs shed directly into the warm sea-water. 



