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VIII. On the Experimental Hyhridization of Echinoids. 



By Cresswell Shearer, Walter de Morgan, and H. M. Fuchs. 



Communicated hij Prof. J. Stanley Gardiner, F.K.S. 



(Eeceived March 11,— Kead May 8, 1913.) 

 (From the Laboratorj' of the Marine Biological Association, Plymouth.) 



[Plates 19-25.] 

 Contents. 



PAGE 



1. Introduction 255 



2. Literature 258 



3. Material 265 



4. Physical Conditions of Sea- Water, etc 271 



5. Methods 273 



6. Characters of Pure-bred Plutei 277 



7. Detailed Description of Typical Cultures of 1910 282 



8. Inheritance of the Larval Skeletal Characters 286 



9. Inheritance of late Larval Characters in 1909-11 301 



10. Inheritance of late Larval Characters in 1912 305 



11. Characters of the young metamorphosed Hybrid Sea-urchins and the Inheritance of 



the same 309 



12. Experimental Control of Dominance 312 



13. Cytology of Cross-fertilized Echinoderm Eggs 315 



14. Sea Temperature as affecting Inheritance 323 



15. Characters of the Hybrid Sea-urchins at the end of the First Year of their Existence 329 



16. General Discussion 338 



17. Conclusions 345 



18. Bibliography 347 



19. Description of Plates 353 



1. Introduction. 



The present work was originally undertaken some four years ago, with the object 

 of finding out how readily some of our common sea-urchins could be crossed, and 

 their larvae reared to a stage when they assumed adult characters. The forms 

 selected for this purpose were Echinus acutus, E. escidentiis, and E. miliaris. One 

 of our number (de Morgan) had already reared the larvae of E. esculentus and 

 E. miliaris, as well as the crosses E. acutus $ X E. escidentus ^ and E. miliaris $ 

 X E. esculentus <^ through metamorphosis. Our early experiments showed that if 

 the right conditions were observed, all the possible crosses between these forms 



vol. CCIV. B 310. Published separately, January 14, 1914. 



