134 



REPORTS ON INVESTIGATIONS AND PROJECTS. 



more important part in the development of the lymphatic system of turtles 

 than we have hitherto supposed. The present series of investigations is 

 being carried on by using both the injection and wax-reconstruction methods 

 in the hope that by using one method to check the other accurate results may 

 be reached. 



Experiments in Bchinoderm Hybridisation, by David H. Tennent, Bryn 



Maivr College. 



During my stay at Tortugas I repeated and verified my observations of 

 1909 concerning the control of dominance by a change in the concentration 

 of OH ions in the sea-water. 



The cross- fertilizations between Hipponoe (Tripneustes) and Toxopneus- 

 tes were made in ordinary sea-water with the facility of the previous summer^ 

 and (as before) there was a preponderance of Hipponoe characters, indi- 

 cated by fenestrated and by multiple anal arm-rods. An additional evidence 

 of Hipponoe influence was shown in the culture of 1910, namely, by the 

 "basket" which is formed by the union of the dorsal and ventral body-skele- 

 tons in purely-bred Hipponoe plutei. This structure did not appear in the 

 hybrid larvae of 1909. 



The Hipponoe characters were not responsive, in the same degree, to the 

 addition of the same amount of acid to the sea-water as in 1909. A further 

 reduction of the OH ion concentration brought results similar to those orig- 

 inally obtained. This is another example of the normal variation in environ- 

 ment which has been the cause of some of the confusion in the recorded ob- 

 servations of the various investigations, made in the same localities but in 

 different years. 



The following table summarizes the investigations on the Toxopneustes X 

 Hipponoe cross. It shows clearly that the efifect of the reduction in alkalinity 

 has been to decrease the Hipponoe characters and to increase the Toxop- 

 neustes characters. 



Summary of Results of Cross-fertilisation. Toxopneustes 9 X Hipponoe $. 

 [Number of plutei studied in each series, 50.] 



These investigations have furnished proof of the possibility of controlling 

 the appearance of certain characters by a change in environment. My ob- 

 servations, together with those of Herbst, show that there is an optimum 

 environment for the occurrence of definite characters. This environment is 

 a complex of factors. Two of the factors are temperature and OH ion 

 concentration. 



