ECHINODERM HYBRIDIZATION. 



BY DAVID HILT TENNENT. 



In 1907 I began work in the field of Echinoderm hybridization, 

 primarily with the object of obtaining material for a study of the be- 

 havior of the nuclear material in cross-fertilized eggs. Some phases of 

 the subject, which in the beginning occupied a secondary place in my 

 mind, have compelled my attention up to this time. The results of 

 these investigations, although incomplete in many ways, are here pre- 

 sented. The study of the nuclear activities will be completed as rapidly 

 as circumstances permit, the mass of my material for this study now 

 being relatively large. 



Those who are at all familiar with this subject realize that a knowl- 

 edge of facts which can be determined only by cytological studies is 

 absolutely necessary before we can reach a definite conclusion regarding 

 the^ phenomena which are described and discussed in this paper. My 

 own results (Tennent 1908) and the later and more complete observa- 

 tions of Baltzer (1909 a and 6) and of Herbst (1909) have shown that we 

 may expect much from further investigations. 



In 1907 at Beaufort I succeeded in making eight crosses, 



i. 



2. 



Arbacia punctulata 9 X Mellita pentapora d\ 



2. Arbacia punctulata 9 X Moira atropos tf. 



3 . Mellita pentapora 9 X Moira atropos d 1 . 



4. Moira atropos 9 X Arbacia punctulata d 1 . 



5. Moira atropos 9 X Mellita pentapora d 1 . 



6. Moira atropos 9 X Toxopneustes d 1 . 



7. Toxopneustes 9 X Mellita &. 



8. Toxopneustes 9 X Moira d 1 . 



In 1908, having realized since the work of the previous summer the 

 absolute necessity of a more complete knowledge of variation occurring 

 in plutei raised under laboratory conditions, I made a study of the 

 development of Toxopneustes variegatus from the fertilized egg through 

 the metamorphosis of the pluteus into the adult. The account of that 

 study of variation is now in press and will appear in the Journal of 

 Experimental Zoology. During the same summer the study of the 

 Toxopneustes-Moira cross was continued and some of the plutei derived 

 from this cross were kept alive and in good condition for 45 days. 



I wish to express my thanks to the Hon. George M. Bowers, U. S. Commis- 

 sioner of Fisheries, for the privilege of working in the Beaufort Laboratory, at 

 which this work was begun, and to Mr. Henry D. Aller, Director of the Labo- 

 ratory, for many courtesies extended to me. I wish also to express my thanks 

 to the Carnegie Institution of Washington and to Dr. A. G. Mayer, Director of 

 the Marine Laboratory at Tortugas, for the splendid opportunity for continuing 

 my investigations and for assistance in completing the plates which are used in 

 illustrating this article. Most of the figures were drawn from the author's sketches 

 by Mrs. Mary T. Walter or by Mr. K. Morita. 



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