266 A. RICHARDS. 



sap also becomes completely diffused into the cytoplasm by 

 this time, and no distinction can be seen. The final event lead- 

 ing up to the formation of the plate is a change in position of 

 the chromosomes with the reference to the axis of the spindle. 

 Previously oriented with their axes parallel to that of the spindle, 

 they now come to lie at right angles with their free ends pointing 

 towards the periphery. When this stage has been reached the 

 plate is fully formed. 



Thus it is possible to follow out the history of the chromosome 

 group in the early cleavages of Fundulus without a single break 

 in the continuity from the metaphase of one generation to that 

 of the next. It should perhaps be pointed out again that this 

 account refers to no particular mitosis. In all of the early 

 cleavage divisions in which the nuclear structures are large enough 

 for study the facts are as here related. 



Since making the above observations on Fundulus the writer 

 has been able to extend them to many stages of the eggs of 

 Corregonus albus, and to satisfy himself that the behavior of 

 nuclear structures is essentially similar in both fish. 



Figs. 26 to 29 do not add any direct proof to the theory of the 

 continuity of the chromosomes, but they serve to throw a side 

 light on the process of spindle formation, at least as it occurs in 

 the gastrulae of this form. The writer has not seen the same 

 conditions in the early cleavage cells and does not presume to 

 claim that they occur there, but since the gastrula shows these 

 rather unusual phenomena, they may be set forth here to assist 

 perhaps in the interpretation of similar appearances elsewhere. 

 At the beginning of the prophase, the formation of the central 

 spindle takes place between the centers that are here divided 

 and are passing to the opposite side of the nucleus. This proc- 

 ess, it will be noted, occurs at a relatively later period in the 

 division of the gastrula cells than in the earlier cleavage cells. 

 Fig. 27 is a face view of a spindle of this type a little farther 

 developed ; certain of the chromosomal vesicles become separated 

 to make way for the developing spindle which gradually sinks 

 down between them and is thus ready for the attachment of the 

 fibers to the chromosomes whenever the latter are formed. It 

 might be thought by analogy with such forms as Crepidula that 



