No. 2.] THE EGG OF BUFO LENTIGINOSES. 299 



granules around the upper pole which gradually becomes 

 thinner towards the equator (PI. XXVIII, Fig. i). Beyond 

 this point the Qgg usually appears unpigmented, although sec- 

 tions through the egg often show a narrow zone of light brown 

 pigment around the periphery of the lower hemisphere. Scat- 

 tered pigment granules are found throughout the egg, being 

 much more numerous above than below the equator. 



The yolk, as in other amphibian eggs, is composed of yellow- 

 ish round or oval granules, which vary greatly in size, some 

 being three or four times as large as others. In general, as 

 Fick has stated, the size of the yolk spherules increases from 

 the dark to the light pole ; but large granules are always found 

 in the vicinity of the germinal vesicle, and are often massed 

 around the first polar spindle after it has reached the periphery 

 of the egg, in the latter case furnishing a means for determin- 

 ing the position of the spindle under a very low magnification. 

 Between the yolk and pigment granules is a loose network of 

 finely granular cytoplasm, which is most abundant in the upper 

 part of the egg. 



At various points, particularly in the upper hemisphere, the 

 yolk-membrane is separated some distance from the surface of 

 the egg, and in the spaces thus formed there is often found a 

 slightly granular substance, the so-called " perivitellin." Some- 

 times this same substance is found in the pigment layer just 

 beneath the surface of the egg (Fig. 2, P). Fick seems to be 

 the only investigator thus far who has discovered perivitellin 

 in the unripe ovarian egg, although von Baer ('34), Hertwig ('76), 

 Schultze, Jordan, and van Bambeke find it in the amphibian 

 egg, and van Beneden ('75) in the rabbit egg, after maturation 

 is completed. All these investigators consider this substance 

 to be a portion of the germinal vesicle which has been forced 

 out of the egg, perhaps by contractions of the yolk, as sug- 

 gested by Hertwig. 



As far as can be judged from its reactions to various staining 

 fluids, the perivitellin of the ovarian egg of Bufo has exactly 

 the same structure as the substance which is found around the 

 lower part of the germinal vesicle at this period (PI. XXVIII, 

 Figs. I, 3, CY). The presence of perivitellin at this stage of 



