536 



SCIENCE 



[N. S. Vol. XXXVII. No. 953 



order out of the apparent confusion in which 

 the subject of Echinoderm hybridization is 

 involved. 



I may preface my remarks by saying that 

 actually no confusion exists. The apparent 

 confusion is the result of too narrow and re- 

 stricted a view of the facts, but the student of 

 genetics whose attention has not been called 

 in detail to the matter has no means of realiz- 

 ing that this is true. 



In at least two published papers I have made 

 in substance this statement: 



It is well known that an apparent confusion 

 exists among observations on hybrid Echinoid 

 larvffi, as to whether plutei of a maternal type, a 

 paternal type or of mixed form are derived from 

 certain crosses. Different results have been ob- 

 tained by different investigators and by the same 

 investigators working in different regions or in 

 the same region in different seasons. 



This statement was made after the consid- 

 eration of the work of Boveri, Driesch, Mor- 

 gan, Seeliger, Vernon, Doncaster, Herbst, 

 Steinbriick and others, in connection with 

 my own observations, extending at that time 

 over a period of five years, which were based 

 upon some fifteen successful crosses. 



If further proof of the truth of the quoted 

 statement be needed we have it in the results 

 of Hagedoorn, who wrote in 1909 on the 

 " Purely Motherly Character of the Hybrids 

 produced from the Eggs of Strongylocentro- 

 tus," and of Loeb, King and Moore, who in 

 1910, after working on the same type of ma- 

 terial, in the same region, reached the conclu- 

 sion that the hybrids show neither a prepond- 

 erance of paternal nor of maternal influence. 



Again, Shearer, De Morgan and Fuchs in 

 1911 published a " Preliminary Notice on the 

 Experimental Hybridization of Echinoids," 

 based upon three years' study of three species 

 of Echinus, in which they state the conclu- 

 sion " that the inheritance of the late larval 

 characters was invariably maternal." In 

 1912, after another year's work on the same 

 forms they published in the Quarterly Jour- 

 nal of Microscopical Science, Vol. 58, 



To our surprise, however, the behaviour of some 

 of the hybrids has differed greatly this season 



from that of previous years. In late larval life 

 some of the hybrid crosses have shown as strictly 

 a paternal inheritance as in previous years they 

 have shown a maternal one. 



It is perfectly evident then that the observa- 

 tions of these later students confirm the 

 truth which I have been trying to establish 

 from my own work, as well as urging that it 

 had already been established by earlier in- 

 vestigators. I emphasize again then the fact 

 that no actual confusion exists. It has been 

 established again and again that under some 

 conditions we may obtain larvee of a maternal 

 type with respect to certain characters, under 

 other conditions larvse of a paternal type and 

 under still other conditions larvse of a blended 

 type. This is established. We should accept 

 the fact. 



The real problem in Echinoderm hybridiza- 

 tion is the determination of the conditions 

 under which these various types appear. 



Another idea to which I wish to call atten- 

 tion is embodied in a statement in the sum- 

 mary of the Shearer, De Morgan and Fuchs 

 1911 paper : 



As the result of extensive investigation of the 

 early larval history of our various crosses, we have 

 come to the conclusion that these are too variable 

 to afford any definite evidence of parental influ- 

 ence and especially is this true with regard to the 

 skeleton, heretofore considered the chief index of 

 inheritance. 



This generalization from a few crosses 

 should not be applied to aU. I am very will- 

 ing to admit the statement for the Shearer, 

 De Morgan and Fuchs crosses. I can not ad- 

 mit it for some of my own. 



In my investigation of the variation of 

 Echinoid plutei I made a prolonged study of 

 the skeleton of Toxopneustes plutei. I know 

 what the variations in the skeleton under lab- 

 oratory conditions are, and I determined 

 these variations before drawing my final con- 

 clusions as to the character of the skeleton in 

 hybrids. When the extent and nature of the 

 variations in the skeleton have been deter- 

 mined it may well serve as one of the indices 

 of inheritance in crosses. 



Further than this, in proper material, pa- 



