EXPLANATION OF PLATES 



All figures were drawn with the aid of a camera lucida. The optical equip- 

 ment consisted of a 1.8 oil-immersion objective with a no. 8 ocular. The draw- 

 ings, made at table level, at a magnification of 1600 X, are reproduced as drawn. 

 It is not possible to produce a drawing in two planes which will show the objects 

 as adetjuately and convincingly as they appear when studied in three planes. 

 Added to this is the difficulty of drawing such minute objects as fish chromo- 

 somes accurately. The drawings are as faithful a representation of the facts 

 as can perhaps be hoped for under these conditions. 



PLATE 1 



EXPLANATION OF FIGURES 



1 to 4 Fundulusheteroclitus 9 X Ctenolabrus adspersus d^. 



1, a and b An anaphase of first cleavage in two sections. Some chromosomes 

 omitted for clearness. All of the lagging chromatin is included in the drawings. 

 Chromosomes of Fundulus are more numerous in a. Ctenolabrus chromo- 

 somes appear in b. 



2, a and b A late anaphase in two sections. Two types of chromosomes can 

 be recognized. There is lagging, but the amount of chromatin involved is less 

 than that in figure 1. Not all of the chromosomes were drawn. 



3, a and b Two sections of one spindle. One split chromosome is seen pass- 

 ing to the lower pole of a. The hooked chromosomes in a are characteristic of 

 Ctenolabrus. 



4 One section of a fairly late anaphase of second cleavage, showing an acute 

 case of irregular distribution of chromatin. This is typical for the rest of the 

 two spindles present in this egg. 



5 to 8 Fundulusheteroclitus 9 X Prionotus carolinus cf'. The chromosomes 

 of both species can be identified in these drawings. The Prionotus type are 

 short rods. There are fewer hooks than were found in Ctenolabrus. 



5 An early anaphase of second cleavage. Only one of the two sections of the 

 spindle is given. Marked lagging. 



6 The middle section of a first-cleavage anaphase that appeared in the prepa- 

 rations in three sections. Some chromosomes omitted. 



7 An early anaphase of the second cleavage. Marked lagging. 



8 An older spindle of the same stage. Only one section drawn. Both types 

 of chromiosomes are seen at the poles. 



416 



