52 J. F. McCLENDON. 



EXPLANATION OF PLATE I. 

 . 1-14, 7Vie Dichelestid. ) 



FIG. I. An Oogonium. 



FIG. 2. Three consecutive primary oocytes in the synapsis stage. Optical section 

 of the cord of ovarian cells. 



FIG. 3. Early growth stage of same, partial disappearance of cell walls. 



FIG. 4. Middle portion of oocyte containing the nucleus, from longitudinal section 

 of oviduct. Commencement of formation of yolk spherules (}>). Two nucleoli are 

 seen (). 



(Figs. J-io, Pandarus siitttatus J'ern//.) 



FIG. 5. A little later stage. Nucleus viewed from the animal pole. Two of the 

 eight double rods, or diads, are joined together end to end (to the right), so that it 

 is difficult to distinguish them separately. 



FIG. 6. The same in a section through the short axis containing six of the diads. 

 Above at n, the nucleolus of another egg is represented to show a later stage in the 

 disintegration of the nucleolus. 



FIG. 7. The first maturation spindle. 



FlG. 8. Later stage of same, in which it has rotated through almost a right angle 

 and is pushing through the egg membrane to extrude the first polar body. 



FlG. 9. Late metaphase o/ the second polar spindle. The first polar body is rep- 

 resented at/. ( Constructed from two sections of the series. ) 



FlG. 10. The same stage from a surface preparation of the egg. The wall of the 

 oviduct was torn off and the eggs allowed to separate in sea water (two hours). In 

 separation the first polar body is pulled out into a stalked structure. 



( Figs. //-//, The Dichelestid. ) 



FlG. II. Less magnified figure of prophase showing sphere of cytoplasm (.r) near 

 periphery of egg. 



FIG. 12. A later stage. The nuclear sap has faded, it is vacuolated, and around 

 each chromosome stains darker (_/") than elsewhere. The two chromosomes that 

 are stippled are out of focus. The chromosomes are ring-shaped tetrads. 



FlG. 13. The chromosomes are each enclosed in a linin sac, and these sacs have 

 begun to elongate. 



FIG. 14. The same or a little later stage. The elongated linin sacs lie parallel, 

 with spindle fibers developed between them. The incipient spindle is formed in 

 dense (dark) protoplasm while this latter is surrounded by looser (paler) protoplasm. 



FIG. 15. Equatorial plate, same stage as 14. 



FIG. 16. The spindle has elongated perpendicular to the short axis of the egg. 

 The dense protoplasm forms the two poles of the spindle. While the loose proto- 

 plasm forms astrosphere-like structures enclosing the poles of the spindle. 



FlG. 17. The spindle is half rotated toward the short axis of the egg and has con- 

 siderably shortened in doing so. 



FlG. 18. Lcemargus muricatus Kroyer. Central portion of the egg containing the 

 first maturation spindle. Metaphase. The spindle fibers do not show in this prepara- 

 tion. Three of the eight chromosomes are in focus, one being seen from the end and 

 appearing smaller than the others. 



