large, having the excess water. When centrifuged in hypertonic sea 

 water ( Photographs 10 to 12 ) the clear layer is small, the mitochondrial 

 layer very thick and the heavy granules, yolk and pigment not well 

 separated. The white half is small, containing less water as compared 

 with the red half (Photograph 12). The red half remains about the 

 same size in hypo- and hypertonic sea water, the change in water con- 

 tent taking place in the white halves. The change in size of the nucleus 

 is easily observed, since it lies in the clear layer in these centrifuged 

 eggs. Compare Photographs 1, 2, with 10, 12. (Biol. Bull. 85:143, 1943.) 



PLATE XV. 



Stratification and breaking of unfertilized eggs when centrifuged in 

 single salt solutions. The left cokimn shows stratification of eggs cen- 

 trifuged at 3,000 X g for two minutes in (1) NaCl or KCl; (3) sea 

 water; (5) MgCla or CaCL. The right column shows amount of 

 breaking apart at 10,000 X g for four minutes in (2) NaCl or KCl; 

 (4) sea water; (6) MgCL or CaCL. The eggs stratify best in cal- 

 cium, and least in potassium and sodium salts (Photographs 5 and 

 1). The order of decreasing stratification (increasing viscosity) is 

 CaCL > MgCL > S. W. > NaCl > KCl. The ease with which they 

 break into halves is in the reverse order, those in NaCl break most 

 readily, those in CaCL least readily (Photographs 2, 4, 6). The ease 

 of breaking must be determined by the eflFect of the salts on the 

 surface layers and not on the interior viscosity of the protoplasm. 

 (Biol. Bull. 89:73, 1945.) 



PLATE XVL 



Miscellaneous. Photographs 1, 2. Electrical method of determining 

 sex, showing spenn and eggs shed from genital pores. 1. Male. 2. 

 Female. 3. Egg showing jelly layer. 4. Jelly layer centrifuged off. 

 5. Amoebocytes, red and white. 6. Hyaline layer centrifuged off as a 

 crescent near lower surface of egg. 7. Development without fertiliza- 

 tion membrane. 8. Twins. 9. Cleavage in sea water lacking calcium, 

 showing clear micromeres. 10. Bloated pluteus caused by not being 

 fed. Photographs 11 to 13 of stained sections of developing eggs. 11. 

 Mitotic figure of first cleavage of whole cell, metaphase. 14. Anaphase. 

 12. Mitotic figure of fertilized red half, metaphase. 15. Anaphase. 13. 

 Mitotic figures of parthenogenetic merogone; note absence of spindle 

 but well fonned asters. In 11 and 14 there are two nuclei; in 12 and 15 

 one nucleus and in 13 no nucleus. (Photograph 6 Biol. Bull. 66:233, 

 1934 no. 2; Photograph 8 Biol. Bull. 78:205, 1940a no. 9; Photograph 10 

 Biol. Bull. 97:290, 1949 no. 14; Photographs 11-15 Biol. Bull. 79:185, 

 1940c nos. 136-140.) 



