136 REPORTS O? INVESTIGATIONS AND PROJECTS. 



An attempt was made to collect tumor and cancer-like growths from the 

 fishes of this region. A large ovarian tumor was taken from a shark, and a 

 gray snapper, Lutianiis griscus, was captured which showed a leiomyoma 

 below the eye. These specimens will be studied histologically later. 



Experiments in Echinoderm Hybridisation, by David H. Tennent, 



Bryn Maivr College. 



During my stay of about two months at the Tortugas Laboratory I con- 

 tinued the investigations on Echinoderm hybridization which I began at the 

 laboratory of the U. S. Bureau of Fisheries at Beaufort in 1907. 



H. M. Vernon's paper (1898) on "The relations between the hybrid and 

 parent forms of echinoid larvae" brought out the interesting fact that there 

 was a seasonal variation in echinoid hybrids. He suggested that the occur- 

 rence of "maternal" hybrids in the summer and of "paternal" hybrids in the 

 winter was due to the relative ripeness of the sexual products used in the 

 crosses. 



Leonard Doncaster (1904), in his paper entitled "Experiments on hybridi- 

 zation, with special reference to the effect of conditions on dominance," con- 

 cluded that temperature is the chief if not the only cause of the seasonal 

 changes observed by Vernon, while Herbst (1906-07), in a careful series of 

 studies on heredity in echinoderms, showed that temperature is a contribut- 

 ing, although not the only determining, factor. In my own completed inves- 

 tigations the material at my command, which I had obtained perforce during 

 the summer only, had given me no opportunity for study along this line. 



It was therefore with much interest that I observed that the plutei result- 

 ing from a fertilization of the eggs of Toxopneustes variegatns by the sperm 

 of Hipponoe esculenta were, in a large proportion, paternal in character. A 

 second surprise came when, on attempting the reciprocal cross, Hipponoe fe- 

 male by Toxopneustes male, I found not only that the cross was easily made, 

 but that it gave "maternal" hybrids. I had, then, a clear case of dominance 

 of one species over another (using the term "dominance" in the sense in 

 which it is applied by Doncaster in distinguishing between prepotency and 

 dominance when referring to individual characters taken separately). That 

 is, a dominance of Hipponoe over Toxopneustes. 



It will be seen at once that the importance of seasonal change in the 

 hybrids, whether dependent on temperature or not, had been appreciably 

 lessened. My problem, therefore, was the determination of the unknown 

 factor, the undetermined factor of Herbst's earlier papers on the subject. 



I had been informed that the sea-water in the Tortugas region gave a 

 decided alkaline reaction. Acting upon this information, I tried the effect of 

 increasing and of reducing the alkalinity of the sea-water and found that in 

 this lay the means of controlling the appearance of maternal or of paternal 

 plutei. 



The skeleton of the plutei was taken as the basis of comparison between 

 hybrid and parent forms, because my work in previous years had shown it 

 to be the least variable character in pure embryos. My observations were 

 principally made upon the form of the anal-arm skeleton, since it is in this 

 particular that the plutei of the two forms mentioned differ most noticeably 

 from each other. 



