LiNViLLB. — Maturation Pulmonatea. 



PLATE 2. 



All Figures are of eggs of Limnaa elodes. 



Fig. 7. First polar cell destroyed. Its position indicated by dotted outline. En- 

 larging of centrosphere begun. Centrosome of sperm-aster divided into 

 two, but surrounded by a single system of astral rays. Sperm-head 

 pointed on side toward the distant sperm aster. 



Fig. 8. First polar cell ; the peripheral centrosphere disintegrating. Deep centro- 

 some surrounded by a small spherical centrosphere ; this surrounded, in 

 turn, by an eccentric larger centrosphere. 



Fig. 9. Transverse section through the peripheral chromosomes of the first 

 maturation spindle. Sixteen chromosomes present. 



Fig. 10. To show large sperm-centrosome and, near by, the slightly vacuolated 

 sperm-head. Another sperm-head at periphery of egg. The polar cell 

 in outline projected on the plane of this section. The egg-nucleus is 

 not shown, as it lies in another section. 



Fig. 11. Second maturation spindle. Sixteen dumb-bell shaped chromosomes 

 (dyads) about to divide by transverse division. Constructed from suc- 

 cessive sections. 



Fig. 12. Only one polar cell (second) recognized. Its relation to egg obscured 

 by accidental presence of a foreign body. Formation of first cleavage 

 spindle. 



Fig. 13. Telophase of second maturation spindle. Deep centrosphere surrounded 

 by an eccentric outer centrosphere. Sperm-nucleus without sperm-aster. 



