138 



REPORTS O? INVESTIGATIONS AND PROJECTS. 



Comparison of Results of Cross-Fertilization in Normal Sea- Water with Results of 

 Cross-Fertilization in Sea- Water of Reduced Alkalinity. 



Hipponoe (^ X Toxopneustes 9 : 



Sea-water 



Sea-water -f acetic acid 



Toxopneustes cf X Hipponoe j: 



Sea-water 



Sea-water -f acetic acid 



These tables may be summarized in equational form 



( 1 ) Normal sea water : 

 Hipponoe 1^ 



Toxopneustes 9 

 Toxopneustes (^ 



= Dominant Hipponoe. 



= Dominant Hipponoe. 



Hipponoe 9 



(2) Sea water + NaOH (increased alkalinity) : 



Hipponoe cf _^ . , -^. 



„ — — ^ =: Dominant Hipponoe. 



Toxopneustes y 



Toxopneustes (^ 



Hipponoe 9 



Dominant Hipponoe. 



(3) Sea water + acetic or hydrochloric acid (decreased alkalinity) : 

 Hipponoe cJ' 



Toxopneustes 9 

 Toxopneustes (^ 

 Hipponoe 9 



= Dominant Toxopneustes. 

 = Dominant Toxopneustes. 



The dominance asserted is not complete. The tendency toward dominance 

 is well shown and it is this tendency which may be directed in the manner 

 described. 



I believe that in these results we have an explanation of the seasonal varia- 

 tions described by Vernon. The changes in the sea-water in the direction of 

 a decrease in alkalinity which I produced artificially, that is, the reduction in 

 concentration of OH ions, probably corresponding to normal variations 

 which are correlated with changes of season. Connected with this is the idea 

 of specific reaction to different concentrations of OH ions, the optimum for 

 Hipponoe lying in a higher, and the optimum for Toxopneustes in a lower 

 concentration. 



Other crosses made were : 



Hipponoe 9 X Cidaris 5 . 

 Hipponoe 9 X Ophiocoma 5. 

 Hipponoe 9 X Pentaceros $ . 

 Toxopneustes 9 X Echinaster $ . 

 Toxopneustes 9 X Holothuria floridana $ . 



None of these crosses were especially successful, the development not go- 

 ing beyond the segmentation stages. 



For the Hipponoe X Toxopneustes crosses material for a cytological re- 

 search was collected. I also collected material for work on the anatomy of 

 Pentaceros. 



