58 CHARLES D. SNYDER. 



from which the volume must be about .00217 mm. 3 , representing 

 a volume reduction of 21.9 per cent. The fertilization membrane 

 on the other hand presented a diameter of 191/1 and therefore 

 enclosed a volume of .00364 mm. 3 ; this represents an increase of 

 volume capacity of 30.8 per cent. 



The above observations are summed up in the following sylla- 

 bus for the purpose of ready comparison. It will be observed 

 that the ratio of diameter and volume changes is roughly as 1 : 2.8, 

 a purely geometrical ratio. 



SUMMARY. 



Percentage Dimensional Changes in Two Species of 

 Echinoderm Eggs. 



Reduction in egg-cytoplasm: 



Of Echinarachnius eccentrica 



By hypertonic salt action in diameter, 12.6; in volume, 



33-3- 

 By insemination (not observed). 



Of Asterina miniata 



By citric acid treatment (not observed). 

 By insemination- in diameter, 7.8; in volume, 22. 

 Swelling of fertilization membrane: 

 Of Echinarachnius eccentrica 



Parthenogenetic (hypertonic salt action) 7 in diameter, 



22.8; in volume, about 62. 

 Normally inseminated- in diameter 26; in volume, 



about 70. 

 Of Asterina miniata 



Parthenogenetic (citric acid treatment) 4 in diameter 



3.9; in volume, about n. 

 Normally inseminated- in diameter 9.3; in volume, 31. 



No special technical procedure was resorted to, to make certain 

 that the eggs in these experiments were always spherical. The 

 writer cannot, therefore, be quite certain that the diameters given 

 above are those of perfect spheres and accordingly that the 

 volumes given are the exact volumes of the eggs observed. If, 



1 The membrane is assumed to be present here and coextensive with the egg- 

 cytoplasm. 



