624 BULLETIN OF THE 



pole. Compare the shape of the nuclei, and the relation to their respective asters, 

 with that of the pronuclei in Fig. 68. The more pointed ends of the nuclei are 

 directed obliquely away from the observer, and the interzonal filaments, which are 

 much thicker in the middle than toward the ends, are so bent as to present to the 

 observer their convexities. 



Fig. 80''. Nearly meridional view of the " primary " half of an egg from an 

 undetermined species of Limax. Each pronucleus contains a single nucleolar struc- 

 ture which greatly exceeds any of the others in size ; it is indicated by its shad- 

 ing, the remaining nucleolar bodies being only outlined. 



Fig. 80°. The second polar globule of the same egg as thai last figured, seen in 

 profile, to show the relation of the vitelline membrane, detached by the hardening 

 reagent, and the interzonal filaments to both polar globule and yolk. 



Fig. 81. Vitellus showing one extensive aster with a homogeneous centre (female 

 pronucleus ?), the rays of which are numerous and slender, and several other less 

 extensive asters with few stout rays. The latter are probably induced by the pene- 

 tration of a corresponding number of spermatozoa into the yolk. Abnormal condition. 



PLATE V. 



Fig. 82. Third amphiaster (A^) after the almost complete disappearance of the 

 pronuclei. A few exceedingly faint outlines (pnl ?) may possibly be traces of pro- 

 nucleoli. An irregular plane of prominent granules (incipient nuclear plate ?) sepa- 

 rates the halves of the amphiaster. Asters flattened in the direction of the axis of the 

 still incomplete spindle. Thickenings (ar') occur near the central ends of many of 

 the rays. The central areas contain numerous prominent granules {aa'). Compare 

 with Fig. 85. 



Fig. 83. Amphiaster of the first segmentation sphere, with very prominent 

 spindle and equatorial zone of fibre thickenings (spm), the latter shown in 



Fig. 84, as they appear when the optical axis corresponds with the axis of the 

 spindle. 



Fig. 85. View from the secondary (vegetative) pole. The asters of A'^ well 

 developed before the complete union of the pronuclei. A few highly refractive 

 granules near the axis of the future spindle (too prominent in the engraving). One 

 of the astral areas is homogeneous, the other contains granules. The rays of the 

 asters present thickenings forming a zone concentric with the area. The external 

 limits of the thickenings are not sufficiently defined. The zones, interrupted two or 

 three times by the absence of thickenings from several neighboring rays, are not 

 quite accurately reproduced. 



Fig. 86. A nearly face view of the amphiaster of the first segmentation sphere. 

 A remnant of the substance of the pronuclei is still visible between the spindle and 

 the animal pole. 



Fig. 87. The egg shown in Figi 86, seen lengthwise of the spindle. The re- 

 mains of the nucleus are more distinct than in the preceding view. No fibre thick- 

 enings (nuclear plate) observed. Compare also Figs. 88 and 89. 



Fig. 88. A slightly more advanced stage than is shown in Figs. 86, 87. The 

 asters nearly cover each other, the line of vision being almost parallel with the 

 spindle axis. The remnant of the nucleus, still sharply outlined, lies near the animal 

 pole, and is surrounded with a narrow zone of non-granular protoplasm. 



