364 Dr. O. Schmidt on CoccoUths and Rhahdolkhs. 



an entire disk. I beg the reader who may have Hackel's work 

 at hand to compare figures 25 (discolith) and 72 (cyatholith) . 

 Both, when looked at from the surface, have the same appear- 

 ance ; and even in 72, e, the margin of the Larger disk appears, 

 like e in 25, as the outer ring. If 72 when placed on the edge 

 appears like figs. 33 and 62, whilst 25 in the same position gives 

 an outline like fig. 44, this is due solely to the fact that in the 

 latter case the inner circle and disk are completely concealed 

 by the outer basin-shaped shield. 



I desired at the beginning to call attention to this important 

 point, as it essentially simplifies the question as to the struc- 

 ture of the coccoliths ; and I will now pass to the special ex- 

 amination. 



In PI. XVI. fig. 15 a coccolith is shown from the flat or 

 ventral side. The individual parts are named as follows by 

 Hackel : — a, central granule ; b, medullar space {Markfeld) ; c, 

 medullar ring {Markring) ; c?, granular ring {Kornerring) ; e, 

 outer ring. I must remark that only in rare cases have I seen 

 the medullar ring otherwise than as in my drawing and as 

 Hackel figures it. It appears to me almost without exception 

 as the simple contour of the medullar space, and only becomes 

 more shaded when the medullar space acquires a more concave 

 form. We now first trace the coccoliths to the development 

 of the granular ring, which frequently becomes a granular dish. 

 Numerous corpuscles with a simple or double contour, and 

 from O'OOl to 0*004 millim. in diameter, appear as isolated cen- 

 tral granules and as central granules with the medullar space 

 (figs. 1,2). The most important stage, however, in the deve- 

 lopment of the coccolith is that of the formation of the granular 

 ring. Hackel characterizes this simply as a granulated zone ; 

 and, according to his figures, the material examined by him 

 was already so much altered that the composition of the 

 granular ring of actual spherical portions did not distinctly 

 appear. Bodies like fig. 3 of our plate are not unfrequent. 

 It consists of a lenticular central part, with a ring of from 7 

 to 10 balls. Hackel also has a similar structure in his fig. 10, 

 which, however, according to his statement, consists of merely 

 sarcodic granulations. The bodies of which I am speaking 

 are solid^ but may certainly have proceeded from a sarcodic 

 foundation. 



Although we may remain in doubt as to this categoiy of 

 corpuscles, this is no longer the case with another very frequent 

 form. In fig. 4 we see the central granule and medullar 

 space sun-ounded by a distinct circlet of balls ; and from a com- 

 parison of a great number of specimens and stages, it appears 

 that this ring of globules originates in a growth and subse- 



