No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 423 



the nodal points of a " Wabenwerk " in the sense of Biitschli). 

 This intracellular membrane is not open at any point, and 

 a longitudinal section of it shows it to be not spherical but 

 oval in outline, the apices of the oval being furthest removed 

 from the nucleus. It is present only in the second stage of the 

 nucleolus, and between it and the nucleus no yolk balls occur. 

 I have never seen such a structure in any other egg cells except 

 in the ova of Gryllns abbreviatus ; a similar structure was found 

 by van Bambeke ('83, eggs of Leiiciscus, Lota), Shafer ('80, tgg 

 of Lepus)y and Gerould ('96, Caudina Q.g^. 



4. Tetrastenuna catenulatuni (Verr.) Montg. 

 (Plate 23, Figs. 103-133; Plate 24, Figs. 137-139-) 



The formation of the yolk may be spoken of first, then the 

 nucleoli proper, and afterwards certain large nuclear structures 

 which may or may not represent nucleoli of another kind. 



The yolk first appears in the form of one or two yolk balls 

 {Yk. BL, Figs. 107, 108, 112, 114-116) in the cytoplasm; 

 the larger ones are regularly oval as a rule, and the smaller 

 ones spherical. A number of these yolk balls are produced 

 successively in each cell, and by their fragmentation the ulti- 

 mate yoke spherules ( Yk. Gl.) are evolved. Each such ball is at 

 first smaller than the nucleus of the cell in which it occurs, but 

 gradually increases in size, though the maximum size which it 

 may attain is not a fixed quantity, but is quite variable. As it 

 increases in size it also gradually becomes more deeply stained, 

 attaining its most intense staining when it has attained the 

 limit of size. The substance of these balls is dense, finely 

 granular, not brittle, somewhat refractive ; in the youngest 

 stages of their formation they often appear nearly homogeneous. 

 About the time a ball has reached its maximum size it com- 

 mences to change both structurally and chemically, vacuoles 

 appear in it, it begins to stain less intensely, and becomes 

 irregular in outline. Thus it becomes either coarsely granular, 

 or else unstaining vacuoles appear scattered through it, and 

 with eosin stains no longer a deep red, but a light red or even 

 yellowish. Next it breaks into a number of pieces, whereby 



