124 Papers from the Marine Biological Laboratory at Tortugas. 



figs. 1 , 2 , 3 , and 4) . He also fertilized fragments of Sphcerechinus eggs with 

 Echinus sperm and obtained hybrids of three kinds: (i) Hybrids of the 

 same size as the ordinary larvae but intermediate in form. (2) Dwarf 

 larvae of mixed form. (3) Dwarf larvae of pure Echinus type. 



Boveri concluded that the dwarf larvae of pure Echinus type had 

 been derived from the fertilization of enucleated Sphcsrechinus egg 

 fragments and that the experiment showed the lack of cytoplasmic 

 influence. 



Seeliger (1894) and Morgan (1895) criticized this conclusion, Seeliger 

 showing that in the Sphccrechinus 9 X Echinus o^ cross all of the larvae 

 were not of an intermediate but that some were of the paternal type, 



Fig. I. — Side view of pluteus of 



Echinus microtuberculatus 



(Boveri). 



Fig. 2. — Pluteus of Echinus micro- 

 tuberculatus 

 (Boveri). 



and that in Boveri 's experiments dwarf larvae"'of the Echinus type might 

 have been derived from nucleated fragments. Morgan found that 

 among the crossed larvae a large percentage showed the ynveJEchinus 

 form. Steinbriick (1902), in his study of Sph(srechinus '^ X Strongy- 

 locentrotus (S" crosses, concluded that hybrids are not always of a mid- 

 form, but show an extraordinary variability and exhibit a complete 

 series between paternal and maternal form. In my own investigations, 

 in certain circumstances, I have found a complete series and I have 

 found that it is possible, by changing the environment, to increase or 

 decrease the percentage of larvae resembling one or the other parent. 



To Boveri himself, while admitting the validity of the criticisms 

 of his original proposition, must be given the credit of furnishing us 

 with a rational interpretation of these variations, based on cytological 



