DEVELOPMENT OF THE EGG OF CLAVA LEPTOSTYLA. 2 17 



be particularly mentioned : (i) The entire absence of any correla- 

 tion between the pigmentary zone and the course of cleavage ; 

 (2) the continuous development of pigment, even after the com- 

 pletion of cleavage, and after the ectoderm has been clearly 

 established ; (3) the staining reactions of the granules after hard- 

 ening is comparable, point by point, with that of yolk granules ; 

 (4) finally, the granules are gradually reduced and resorbed with 

 the growth of the embryo. It is in this way that their disap- 

 pearance from the ectoderm above referred to is to be explained. 

 I think that we may therefore conclude that, at least so far as 

 the problem is concerned with Clnva, its solution is unquestion- 

 ably in the negative. If further warrant be needed for this view 

 I believe it will be found in the later history of these pigmentary 

 granules as given in the following account. 



ORIGIN AND GROWTH OF PIGMENTARY GRANULES. 



As already noted the origin of these pigmentary granules is in 

 the immediate region of the nucleus, and about the time this body 

 reaches the outer periphery of the egg. At first they are of ex- 

 tremely small size, about 0.5 micra in diameter, later growing and 

 reaching in some cases a diameter of 3 to 3.5 micra. For some 

 time they were entirely overlooked in prepared material, owing to 

 improper fixation. Only after fixation with picro-acetic (or to 

 less degree with Petrunkevitch) solutions and staining with iron- 

 haematoxylin on the slide were they adequately differentiated so 

 as to be readily studied. Wilson gives a similar account of this 

 technic in reference to the eggs of Dentalinin (cf. Jr. Exp. Zoo/., 

 Vol. I., p. 9, Figs. 1013, explanations). 



As the granules continue to grow larger there may be distin- 

 guished within their substance what appear to be vacuoles, 

 usually a single one within each granule, occupying an eccentric 

 position. In some respects they exhibit nucleolar-like features, 

 especially in their staining reactions and in their vacuolation. 

 Montgomery ('98) has made similar observations on nemerteans 

 and believes they indicate some sort of genetic relationships be- 

 tween nucleoli, yolk balls and granules. My own observations 

 have not seemed to confirm this last point, though in the case of 

 Hydra there are not lacking evidences which I think would give 



