406 University of California Publications in Zoology. I v °l- (> 



V. Formation of the Compound Egg and Cleavage 

 op the Ovum. 



The formation of the compound egg of Gyrocotyle in the first 

 coils of the uterus has been described above. The completed 

 egg presents the appearance shown in plate 41, figure 47, taken 

 from the fifth coil of the uterus. Cleavage begins very shortly; 

 at the same time the walls of the .yolk cells become less definite 

 and their nuclei fainter. There is no indication of cleavage of 

 the yolk-cells. The mass of cells resulting from cleavage of the 

 ovum appears to be a syncytium (pi. 41, fig. 48) ; this mass 

 increases in size with the diminution of the yolk cells. It is 

 impossible to make out cell walls or to discover any orderly 

 arrangement of the nuclei, in the preparations available. The 

 eggs cannot be made sufficiently transparent for study in toto: 

 and the shells are so resistant that no successful infiltration with 

 paraffine was obtained. The best preparations, and the ones on 

 which these statements and figures are based, w'ere celloidin sec- 

 tions stained with Delafield's hematoxylin. The egg-shells show 

 no opercula, and no trace of hooks on the embryo could be dis- 

 cerned. G. rugosa seems to be the only member of the genus 

 which possesses hooked embryos in uterine eggs. 



The eggs when extruded are surrounded by a gelatinous sub- 

 stance which forms a jelly on contact with sea-water. They are 

 discharged with considerable force. The discharge has been 

 observed repeatedly when the intestine of the host was first slit 

 open, and also when the animal was changed from one solution 

 to another. Eggs are always found in the intestinal contents 

 of Chimaera infected with Gyrocotyle. The eggs when first dis- 

 charged are white and glistening, resembling finely cut sand- 

 grains. They are about .095 mm. by .065 mm. and ellipsoidal in 

 shape. The size varies widely in eggs from the same individual, 

 discharged at the same time, ranging from .075 mm. to .112 mm., 

 in longest dimension. 



The newly discharged eggs do not possess opercula (pi. 38, 

 fig. 41). There is a faint differentiation occasionally seen at one 

 pole of the egg, but nothing which could be definitely identified 

 as an operculum has ever been found in fresh eggs. In speci- 



