FERTILIZATION REACTION IN ECHINODERM EGGS. 265 



12 



16 



FIGS. 10 TO 25. Fertilization of egg fragments. The original surface is indicated 

 by a heavier line. Figs. 10 to 18, fragments of 5. franciscanus. Fig. 10, large egg 

 fragment showing wrinkles in the vitelline membrane; Fig. n, same after insemina- 

 tion; the fragment is rounded and the wrinkles have disappeared; Fig. 12, same 

 later, with membrane elevated on the original surface. Fig. 13, smaller fragment; 

 Fig. 14, same after insemination, showing change of form and disappearance of 

 wrinkles; Fig. 15, same, later, with fertilization membrane elevated on original 

 surface only. Fig. 16, small fragment with entire membrane attached; Fig. 17, 

 same after fertilization; only the characteristic crenations appear; the membrane 

 does not elevate on such small fragments. Fig. 18, extra-ovate of S. franciscanus 

 after fertilization; cortical sphere to left, endoplasmic sphere to right; only the 

 former elevates a membrane. 



FIGS. 19 TO 25. Fertilization of egg fragments of Patiria miniata. Fig. 19, small 

 fragment with entire vitelline membrane; Fig. 20, same after fertilization, showing 

 the characteristic crenations; Figs. 21 and 22, same, later, showing separation of 

 the fertilization membrane; it is continuous with the vitelline membrane. Fig. 23, 

 large fragment of Paliria; Fig. 24, same after fertilization. Fig. 25, large and 

 small fragment left within the same vitelline membrane, shown after fertilization; 

 the small fragment exhibits only the characteristic crenations; the large one has 

 elevated a fertilization membrane. 



