662 JOHN BEARD, 



must be denied. The cells within it appear to me to furnish as 

 typical examples of chroraatolysis as one could wish. 



Finally, Rückert noted the practical absence of his megaspheres 

 in the posterior part of the embryo, a fact of much significance to 

 be commented on in the present work. 



Without searching through the vast literature of piscine develop- 

 ment anew, only other two authors can be recalled as having definitely 

 referred to the megaspheres in an attempt to interpret them. H. Ernst 

 ZiEGLER ('96, p. 367) endeavours to explain the megaspheres as the 

 accidental products of an allotment of too much yolk during the 

 cleavage. His exact words are not quoted. His surmise is very wide 

 of the mark and not a revelation at all of their true nature. He 

 also comments upon their frequently large size, their abnormal 

 chromatin-network, amitotic division (without having witnessed it); 

 and, adding that their fate is unknown, suggests that they degenerate. 



C. K. Hoffmann, recording them in certain layers of the embryo, 

 interprets them as cells, which have wandered at a later period from 

 the yolk to take part in the formation of the embryo. There is not 

 a particle of evidence supporting this view. 



With the reservation rendered necessary by the vagueness of 

 what is understood by a megasphere, I am strongly inclined to identify 

 Rückert's megaspheres as germ-cells, or, at any rate, as the normal 

 or abnormal forerunners of such. 



Before the formation of the embryo it will be difficult to pick 

 out the germ-cells with absolute certainty by their size, or by the 

 amount of contained yolk. The twin-character of the nucleus must 

 be the deciding point. So that in the pre-embryonic period for the 

 time being one can only identify as future normal germ-cells those 

 large cells, which possess this peculiarity; and, as already abnormal 

 germ-cells those "megaspheres", which exhibit the multinucleated con- 

 dition, or budding, or chromatolysis. 



When we come to deal with the megaspheres within an embryo, 

 or those within a blastoderm, on which a definite embryo rests, i. e., 

 in skate of 6 mm whose medullary folds have recently closed, we are 

 on safer and more certain ground. In nearly every case we find some of 

 Rückert's megaspheres, and these — practically without exception 

 — after very prolonged and careful examination and consideration I 

 identify as germ-cells, or the immediate forerunners of such. 



Apart from normally placed germ-cells, a varying number of these 

 megaspheres may be found on proper staining in nearly every skate-embryo 



