CHAP. XIII 



EOTIFEEA 



419 



These eggs have a somewhat sticky exterior and are apt to 

 become coated with particles of dust, etc. If the water in which 

 they he is kept clean and changed, they will develop perfectly 

 normally until the perfect Eotifer hatches out. Most o'f Zelinka's 

 observations seem to have been made on the living egg The egg 

 and Its surrounding case are of an oval shape, and at one end there 

 is a fine circular line in the shell, the plane of which is at right angles 

 to the long axis of the egg. This marks the spot where the end of 



Fia. 330.- 



-Early stages iu the segmentation of the egg of Callidina russeola. 

 (After Zelinka.) 



A, 2-ceU stage from the side, before rotation. B, 2-cell stage from the side, after rotation. C, D, 

 3-cell stage and preparation for 4-cell stage, from dorsal surface. E, 4-cell stage, from the dorsal 

 surface. p.&, polar body. 



the egg-case will come off, as it does, in a lid-like manner, and where 

 the embryo will emerge. 



The development is parthenogenetic : no male has yet been found 

 in the case of Callidina. Five hours after the egg is laid a single 

 polar body of comparatively large size is given off from the upper 

 pole. It does not remain here, however, but rotates, along with the 

 general contents of the egg, on to a surface which eventually turns 

 out to be the dorsal surface of the embryo (Fig. 330, B). 



Before this has happened the egg-nucleus has retreated from the 

 spot where the polar body was given off, to the centre of the egg. 



