DEVELOPMENT OF THE ALBINO RAT Zou 
first segmentation spindle are by inference derived from the 
sperm centrosome. The data here given, as concerns the matu- 
ration and fertilization phenomena pertaining to the albino 
rat, unless otherwise credited, have been drawn from the account 
of Sobotta and Burckhard, whose account is accompanied by 
excellent figures. 
Long has studied in living ova of mice and rats the phenomena 
of maturation and fertilization. Tubal ova were placed in Ring- 
er’s solution on an especially constructed slide and spermatozoa 
introduced. It was possible to seminate the ova of rats with 
rat spermatozoa and to observe the formation of the second 
polar body. The formation of the second polar body, ‘‘usually 
near the first polar cell, may begin within five minutes to two or 
more hours after the spermatozoa are introduced. The con- 
striction may be finished three-fourths of an hour later.’ “The 
first appearance is an elevation clearer than the rest of the cell. 
The swelling becomes higher, and at one side of the elevation 
there appears a depression which is the beginning of the constric- 
tion which presently encircles the whole swelling and cuts it 
off from the egg.’’ Nothing couldbe said as to the changes which 
the chromatin undergoes after the spermatozoa have penetrated 
the egg. The eggs remained alive and apparently normal for 
about twelve hours, after which they began to degenerate. 
PRONUCLEAR] STAGE 
As has been stated, my own observations on the develop- 
ment of the albino rat (Mus norvegicus albinus) begin with the 
pronuclear stage. The material at hand for this stage is listed 
in table 1, page 258. 
Thus there are present in the series 34 ova showing a pro- 
nuclear stage and 9 ova showing the second maturation spindle 
in the monaster phase. The latter may be dismissed with the 
brief statement that they represent unfertilized ova. In rat 
No. 108, with 7 ova in the stage of the second maturation spindle, 
killed 24 hours after the observed copulation, there was found 
no trace of spermatozoa in the oviduct. Two reasons may be 
offered for the non-appearance of fertilization in this case: 
