Echinoderm Hybridization. 



125 



studies (Zellen-Studien 5 and 6), and it is on the basis of this interpre- 

 tation that the more recent work of Herbst, Baltzer, and others is 

 founded. 



The beginning of a second phase of work in Echinoderm hybridiza- 

 tion was marked by the appearance of Vernon's papers. As a preparation 

 for his work on hybridization, Vernon (1895) made a careful study of 

 the effect of environment on the development of Echinoderm larvae, 

 using Strongylocentrotus lividus as the subject of his research. As means 

 of changing the environment he used (i) Differences in temperature, 

 (2) Differences in concentration of sea -water, (3) Differences in light, 

 (4) Chemical agents. 



Strongylocentrotus eggs were placed in water of 8 or 25 C. for an 

 hour, or even for a minute, at the time of impregnation. After 8 days 

 the resulting plutei were 4.4 per cent smaller than those from eggs 



FIG. 3. Pluteus of Sphccrecliimts 



gramdaris 



(Boveri). 



FIG. 4. Hybrid pluteus Eclihms 

 microtitberculatus c? X Sphcere- 

 chinus granularis ? 

 (Boveri). 



fertilized at 17 to 22 C. Larva? allowed to develop in water 17 to 

 22 C. were 2 per cent or more larger than those allowed to develop at 

 temperatures above or below these limits. 



The normal breeding season of Strongylocentrotus is from December 

 to March. Larvae from fertilizations made in August were 20 per cent 

 smaller than those obtained in April, May, or October. June and July 

 larvae were intermediate in size this due to immaturity. 



The addition of 50 c.c. distilled water to a liter of sea-water gave 

 larvae 15.6 per cent -larger than larvas grown under normal conditions; 

 25 c.c. distilled water to a liter of sea-water, 9.5 per cent larger; 150 c.c. 

 distilled water to a liter of sea-water, 4.3 per cent smaller. Larvae 

 developed in more concentrated sea -water were unchanged; larvae grown 

 under normal conditions from impregnations made in concentrated sea- 

 water were 1.6 per cent larger. Larvae grown in semi-darkness were 

 2.5 per cent larger; in darkness 1.3 per cent smaller; in blue light 

 (copper sulphate), 4.5 per cent smaller; in violet blue light (Lyons blue), 



