Plate II. 



Fig. 21. The same ovum as in the preceding plate, though slightly later. The segments have sepa- 

 rated again. Seen from above. 



Side view of an ovum with four segments. 



The same ovum as in figure 21, at one hour and 55 minutes after the fecundation. The 

 eight segments are in a state of compression against each other. Seen from above. 



The same ovum as in figure 22 though later and with eight segments. Side view. 



The same ovum as in figure 23 at two hours and 20 minutes after the fecundation. Sixteen 

 segments: four micromeres, tour »large» macromeres and eight »small» maoromeres. 

 Seen from above. 



The same ovum as in figure 2i though later and with sixteen segments. Side view. 



The same ovum as in figure 26 though later and with thirty-two segments. Side view. 



Optical section of the same ovum as in the preceding figure. 



The same ovum as in figure 25 at about two hours and 35 minutes after the fecundation. 

 Stadium with thirty-two segments. Seen from above. 



The same ovum as in the preceding figure at about three hours after the fecundation. 

 Stadium with sixty segments. Seen from above. 



Ovum at about seven hours after the fecundation. The egg has changed into a Blasto- 

 sphere with a diameter of about 0,i mm. Optical section. Several blastomeres are in 

 a state of division. Stained with Grubler's acetic acid carmine. 

 » 32. Blastula at about thirteen hours after the fecundation, stained with Grubler's acetic acid 

 carmine. Several cells are in a state of division. The cilia have protruded. The larva 

 is still enclosed within the mucilaginous coat. Length = O.14 mm. Breadth = 0,o9 mm. 

 » 33. Blastula at about twenty hours after the fecundation. Optical section showing how the 

 wandering cells loosen from the vegetative pole and arrange themselves in the bla- 

 stocoel. Length = O.19 mm. Breadth = 0,09 mm. 

 » 84. Young Gastrula at about twenty-five hours after the fecundation. The first pair of cal- 

 careous deposits have arisen. Optical section. Length = 0,23 mm. Breadth = 0,ob ram. 

 » 35. Blastula at about twenty-five hours after the fecundation. Two calcareous stars have begun 



to arise. Optical section. Length = 0,) mm. Greatest breadth = 0,i mm. 

 B 36. Blastula at about thirteen hours after the fecundation, developed from the egg repre- 

 sented in figure 30. Optical section to show the wandering cells. The larva is still 

 enclosed within its mucilaginous coat. 



