122 CKESSWELL SIIEAREK, WALTER DE MORGAN, H. M. FUCIIS. ' 



different Echinoids, making use of Sphacrecliinus eggs and Ecldiius 

 sperms at Naples. He found that the hybrid larvae were intermediate 

 between those of the two parents. In 1894 Seeliger (16) made the 

 same cross at Trieste, but found that many of his hybrids were of the 

 purely paternal type ; thus contradicting Boveri's result. In the 

 following year Morgan (12) repeated this work, getting the same 

 results as Seeliger. In 1895 Boveri (4) replied to Seeliger and 

 Morgan substantiating his earlier results, but suggesting that at 

 Trieste the Plutei had other characteristics from those at Naples. 

 This does not apply, however, to Morgan's results obtained at Naples 

 on the same material as that used by Boveri. 



In the same year Vernon (19) commenced a new era in the work by 

 a thorough investigation of the effects of environment on the laiViB. 

 In 1898 he followed up his first work with the investigation of inheri- 

 tance in various hybrid forms. He made crosses between Sphacrcchiii ».-;, 

 IStrongylocentrotvs and Echinus. His hybrid larva? were mostly 

 maternal, but some species seemed to have a greater capacity for 

 transmitting their characteristics than others. In the same year 

 Driesch (6) crossed Strongylocentrotus, Sphaerechinns, Echinus, and 

 Arhacia and obtained hybrid larvte of a purely maternal type. 



In 1900 Vernon (21) hybridized Strongyloccntrotns and Sphacrcchiiins 

 at Naples and claimed to find that the parental influence in the resulting 

 hybrids varied with the season of the year at which the experiments 

 were made. In spring they resembled Strongiiloccntrotus, while in 

 summer they were like Sphacrechimis. In the latter case, however, 

 none of the larvae were of the pure Sphaerechinus type. He suggested 

 that this variation was due to a seasonal fluctuation in the relative 

 ripeness of the sexual products. 



In 1902 Steinbriick (17) studied the cross Strongylocentrof us S x 

 Spliacrcchinus J and came to the conclusion that, while there was 

 a seasonal variation in dominance, it was not due to the relative ripe- 

 ness of the eggs and sperm, but to changes in temperature ; for, by 

 raising the temperature of the water in which his larva were kept, 

 in the spring he caused them to assume the summer form. In the 

 same year Driesch (7) did some further work on the hybridization of 

 Stronrjylocentrotus, Sphacrechimis, and Echinus, and substantiated his 

 earlier results of maternal influence. 



In 1906 Fischel (8) working at Villefranche, crossed Arlacia, 

 Echinus, and Strongyloccntrotns and contradicted Driesch, finding that 

 the sperm had an important influence and that the hybrids showed 

 undoubted paternal characters, although these were, he admitted, of 

 a very minor degree as compared with the maternal. 



