130 Papers from the Marine Biological Laboratory at Tortugas. 



applied throughout the gastrula stage if the number of rods with latticed 

 structure is to be increased. 



3. The number of anal arm supports with more than one root is 

 already determined by the gastrula stage, before the triradiate spicules 

 have given rise to rods. In the cultures transferred to warmth at the 

 gastrula stage, there is no such increase in number of arm supports with 

 three or four roots as in warm cultures in which the larvae remain to the 

 completed pluteus. 



Doiicaster (1903) concluded that the different hybrids owe their 

 peculiarities to the temperature of the water in which they developed. 

 Herbst's conclusion (1906) is that Vernon's seasonal variation is partly 

 dependent on temperature. Besides this, another unknown factor has 

 played a role, this factor varying not only during the time of year but 

 also varying in the two years. Herbst feels himself forced upon the idea 

 of a variation of hybrid form which is certainly not connected with the 

 direct influence of temperature in the formation of the larvae. 



THE CONTROL OF DOMINANCE. 



Herbst (1906 6) found a method of controlling the appearance of 

 maternal characters in the combination of parthenogenesis and fertili- 

 zation. By subjecting the eggs of Sph&rechinus to treatment which 

 would cause their parthenogenetic development and fertilizing them 

 with Strongylocentrotus sperm before the nucleus had fairly begun its 

 processes of division, Herbst obtained a displacement of heredity to 

 the maternal side. The method of treatment was much the same as 

 that which I used in a study of the star-fish egg (1906), a method which 

 has also been used by Fischel and by Loeb (1907). The effect of the 

 treatment is shown in the following table; the displacement toward the 

 maternal side (Sphcer echinus) being well marked. 



(Herbst, (19066), Table I, page 482. Anal arm rods, Sph&rechinus 9 X 

 Strongylocentrotus &. Number of plutei studied in each case 50.) 



Herbst suggested that this displacement might be caused by- 



(1) The growth of the maternal nuclear substance. 



(2) An alteration in the condition of the cytoplasm. 



(3) Or both factors together may influence the displacement. 



Pursuing the subject further (1907), he determined the critical stage 

 of displacement. A striking shift takes place when the nucleus at the 



