148 Papers from the Marine Biological Laboratory at Tortugas. 



SUMMARY OF THE CONTROL OF DOMINANCE. 



The outcome of the investigation may be summed up in the form 

 of equations. 



I. Ordinary Sea- Water. 



H ipponoe c? 



T^xopneustes 9 = Dominant mpponoe. 



Toxopneiistes d^ 

 ~ mpponoe y = Dominant H ipponoe. 



II. Sea -Water + NaOH. 



H ipponoe c? 



Toxopneustes 9 = Dominant Hipponoe. 



Toxopneustes d^ 



Hipponoe 9 = Dominant Hipponoe. 



III. Sea-Water + Acetic or Hydrochloric Acid. 



Hipponoe o' 



■f- z J — ^ = Dominant Toxopneustes. 



1 oxopneustes 9 ^ 



Toxopneustes c? . „ 



T_r ■ ^^ ~ ;; = Dommant Toxopneustes. 



Hipponoe 9 ^ 



DISCUSSION OF RESULTS. 



The task of bringing together and of hannonizing the results of 

 various investigators is extremely difficult. Their results are diverse. 

 In many cases the same fonns worked with in the same localities, at 

 the same time of year, but in different years, have given at one time 

 one result, at another time another result. Yet the work has been done 

 by investigators whose ability is unquestionable. 



I may be criticized for having given so full a resume of the papers 

 of Herbst and of Vernon. I have done this for the purpose of giving an 

 exact account of our present knowledge of Echinoderm hybridization, 

 which I hope may be useful. 



I have already stated that I regard the material with which I have 

 worked as especially fortunate, more fortunate than that which has been 

 obtained by any other investigator. This is for two reasons, 



(i) Reciprocal crosses were readily made and the plutei from both 

 were well formed. 



(2) A clear preponderance of Hipponoe characters was evident, no 

 matter which way the cross was made. 



In the resume of the literature of the subject that I have given 

 and in my own work one thing stands out clearly: This is the " optimum." 



Herbst determined an optimum concentration of OH ions in the 

 sea -water of the Gulf of Naples; an optimum OH ion concentration in 

 his cross-fertilization researches; an optimum temperature for develop- 

 ment. Vernon determined optimum temperature, light, season, con- 

 centration of sea-water, etc. My own studies have shown an optimum 

 time for fertilization, an optimum concentration of OH ions, etc. 



Ever3'thing points to an optimum environment and a necessary 

 environment for certain occurrences. This is only what we expect. 

 One aim of scientific research is to determine the conditions in which 

 certain phenomena will be exhibited. Our evidence has shown the 



