260 MESSRS. C. SHEARER, W. DE MORGAN, AND H. M. FUCHS 



plutei, but rather diminished it. Tlie opposite, however, was the case in the reciprocal 

 cross. 



In 1902 Steinbruck (83), from a study of the cross Sphferechinus granularis % X 

 Sti-ongylocentrotus Uvidus $ , came to the conchision that the hybrid larvae showed 

 immense variation, all intermediate examples being present, from the paternal to the 

 maternal types. In some cases he found mosaic inheritance, half the skeleton 

 resembling that of the father and half that of the mother. He studied the skeleton 

 and the outward form, but the latter can have been of little value as he used 

 preserved material. He noted in his pure cultures of Strongylocentrotus the frequent 

 occurrence of multiple rods in the postoral arm skeletons. 



In 1903 Loeb(52) attempted to obviate the difficulty arising from the fact that 

 with the Echinoids used up to that period for experiments in heredity, there nuist 

 always be some doubt concerning the inheritance of characters so much resembling 

 one another. He devised a method which enabled him to hybridize forms so far 

 removed from one another as Asterias and Strongylocentrotus. While the early 

 larvae of the former have no skeleton, those of the latter have one. In the hybrids 

 the skeleton of the maternal form [Stivngyluccntrotus) appeared. 



In the same year Doncaster (21) crossed Echinus microtuherculatus ? X Strongy- 

 locentrotus Hvidus $ , and reared many of the larvae to a late stage and some through 

 metamorphosis. He decided, however, that the parental larval forms resembled each 

 other too much for any conclusions to be based on the characters of the hybrids. 

 Following the example of Vernon, he drew most of his results from the cross 

 Sphmx'chinus gntnuloris $ X Strongyloccntrotiis Uvidus $ , using larvae eight days 

 old, preserved in alcohol. He concluded that there was no evidence that staleness of 

 the sexual products gives a diminution of dominance* of characters. 



He confirmed Vernon's seasonal change in " prepotency," but attributed it to a 

 change in temperature. By raising the temperature in which larvae were reared in 

 spring, he caused them to assume the summer form. 



In 1903, Driesch (26) hybridized Strongylocentrotus Uvidus, Sphcerechinvs 

 granidaris, and Echinus microtuherculatus. Contrary to the conclusions of Boveri, 

 he found, as in his previous investigation, all the characters to be maternal, but 

 he excepted the pigmentation and skeleton, both of which he found to be influenced 

 by the sperm. 



In the same year Boveri (11) criticised Driesch's conclusions, especially with 



* In this and subsequent p<apers of LoEB, King, and Moore (.54), Tennent (88), Debaisieux (16), 

 Moore (64), etc., the term " dominance " is used in a somewhat general sense. It is only in the 

 F2 generation that a segregation can be seen, and as no one has so far succeeded in raising the 

 Fi generation in Echinoderm hybrids to the sexually mature stage, it is premature to apply this term, 

 as is done in these papers, to the Fi generation in the strict Mendelian sense. Dominance in Echinoderm 

 hybridization work therefore is not to be confused with the more restricted meaning usually attached to it 

 in Mendelian work. It corresponds more nearly in Echinoderm work with the older term " prepotency." 



