MUSEUM OF COMPARATIVE ZOOLOGY. 625 



Fig. 89. The same egg as the last, rotated nearly 90° about its primitive axis. 

 The remnant of the nucleus appears less sharply outlined. The elements of the 

 equatorial nuclear plate are very evenly arranged, and conspicuous. 



Fig. 90. A slight furrow introducing the first segmentation of the yolk has made 

 its appearance at the animal pole. A vitelline membrane is detached from the yolk 

 over a space corresponding to this furrow. The nuclear spindle is viewed somewhat 

 obliquely, so that the lateral disks of fibre thickenings are not seen exactly edgewise, 

 and therefore appear oval. The left-hand edge is represented in the lithograph as 

 farthest from the observer ; the right-hand edge of the oval should have been made 

 the fainter, as it is really the more remote. 



Fig. 91. Constriction further advanced than in Fig. 93 ; nuclei much larger ; 

 interzonal filaments distinguishable only near the plane of division between the two 

 secondary cells. Asters becoming less distinct. 



Fig. 92. Equatorial thickenings in the spindle of the first segmentation sphere, 

 as seen when the spindle is viewed lengthwise. 



Fig. 93. Formation of the nuclei of the first pair of blastomeres. Interzonal fila- 

 ments sharply bent and slightly thickened. Compare Fig. 29. 



Fig. 94. Spermatozoon with vibratile (?) membrane. The tail end should have 

 been made thinner. The free edge of the membrane indicated by the sinuous line. 



Fig. 95. View of a portion of a living egg of Limax sp. ? toward the end of the 

 formation of the second polar globule, to show the existence of pseudopodia. 



