768 



The American Naturalist. 



[September, 



The yolk sac seems unusually large, and the tail is comparatively 

 long at this period, but otherwise these tadpoles are externally like 

 those of Rana and Hyla. 



NATURE AND ORIGIN OF THE WRINKLES. 



If the eggs be preserved during the first segmentation while the 

 wrinkles are still present, and then sectioned parallel to a plane tan- 

 gential to the superior pole, considerable additional light is thrown 

 upon this process of wrinkling. 



As has been noted in the eggs of other frogs the pigment is gathered 

 into a thin surface layer over the superior hemisphere. 



Houssay states that the pigment does not characterize this pole, but 

 only happens to be there on account of the coincidence of its density 

 with that of the surrounding protoplasm (Etudes d'Embryologie sur les 

 Vertebres, Archiv. de Zool. Exper., 1890). However this may be, 

 during segmentation pigment appears along the sides of the furrows, so 

 that eventually the resultant cells come to have a more or less definite 

 pigment layer around their periphery, BCoussay accounts for this by 

 saying that there is an intimate relation between the activity of the cell 

 and the presence of pigment. When the resting cell becomes active 

 its granules become smaller, and pigment appears in them as the result 

 of chemical action. 



The presence of pigment, therefore, is the result of an increased activ- 

 ity in the cell. 



But Bambeke tells us that " the cortical layer, when it enters the 

 interior of the protoplasm, is not entirely employed in limiting the 

 spheres of new formation. In fact, I find masses of pigment whose 

 presence can only be explained by considering them as debris from the 

 cortical layer, which has penetrated into the protoplasm " (Fractionne- 

 ment de I'Oeuf des Batraciens, Archiv. de Biologic, Vol. I, p. 346, foot- 

 note). 



An examination of sections of these Chorophilus eggs shows a similar 

 occurrence. 



In addition to the pigment layer which borders the first segmenta- 

 tion furrow, and which is somewhat thicker near the centre of the 

 section, there is also a lunate mass extending downward vertically from 

 the superior pole on either side of the furrow (Fig. 39) and in imme- 

 diate contact with it. This mass can be traced in the sections from the 

 surface layer, in which it has very little area, down somewhat beyond 

 the bottom of the furrow, where it spreads out laterally and is lost in 

 the surrounding protoplasm. In this particular egg the mass does not 



