434 



EDWIN G. CONKLIN. 



EXPLANATION OF PLATE IX. 



FIGS. 49-60 represent eggs which had been subjected to diluted sea-water. 



FIGS. 49-54. No. 859. Sea-water i part, fresh water 2 parts, i hr.; normal 

 sea-water 4 hrs. Eggs were treated with this diluted sea-water during the third 

 and fourth cleavages, thus causing a scattering or stretching out of chromosomes 

 along the spindle and the formation of chromatic connections between daughter 

 nuclei. In cell D, Fig. 49, the division was stopped -in the prophase, the nucleus 

 being pear-shaped with the chromatin chiefly in the narrow upper end of the pear. 

 It is significant that the long axis of the pear is in the direction of the spindle axis 

 and that if the constriction were to separate the neck from the body of the pear, 

 the daughter nuclei thus formed would be of approximately the same size as in 

 normal eggs. 



FIG. 51 shows more advanced stages of a similar process in which the chromatin 

 is chiefly in the smaller, upper nuclei, the achromatin in the larger, lower ones. 



FIGS. 49 and 50 show certain nuclei in which the nuclear membrane remains 

 intact though the chromosomes are arranged along a line or spindle connecting 

 the two centrosomes. 



FIGS. 52-54. Eggs in which the third cleavage took place by a modified form 

 of mitosis which left chromatic connections between daughter nuclei, and yet 

 typical spindles for the fourth cleavage are present in some of the macromeres. 



FIG. 52. In all four quadrants of this egg nuclear division at the third cleavage 

 took place by modified mitosis, the daughter nuclei remaining connected by chro- 

 matic threads; in only two quadrants were micromeres formed, and the macromeres 

 of these quadrants are now dividing by mitosis. 



FIGS. 53, 54. All daughter nuclei are connected by chromatic threads. Chro- 

 matin aggregates on the side of the nucleus next the centrosome (Fig. 54, D) and 

 the chromatic connections between daughter nuclei run to the outer sides of the 

 nuclei and spindles in the macromeres; the latter may be approximately normal, 

 though the spindles may be out of proper position and the chromosomes more or 

 less scattered. 



