312 THE AMERICAN MONTHLY [Nov., 



Karyokincsis in Embryos of the Domestic Cat. 



lU- FRANK S. AHV. 

 IdWA CITY. InWA. 



In all ticctitius of various embryo kittens that have been ex- 

 an)ine«l by the writer, up to those of embryos seventeen milli- 

 meters in lengtli, karyokinetic figures are by no means an occas- 

 ional or a rare occurrence, but are to he fmind in many situa- 

 tions. 



In the preparation of these sections no special teclinique was 

 emjiloyed, as the subject of investigation was the development 

 of tlie central nervous system of the cat. The embryos were 

 hardened in increasing strengths of alcohol, with no precautions 

 whatever with regard to fixation. After remaining in 95 per 

 cent alcohol for a number of months, the embryos were em- 

 V>eded in celloidin and sectioned. The sections were then 

 stained in Grenadier's ha^matoxylin and mounted in balsam. 



The resting nuclei are sometimes spheroidal, but the more 

 usual form is that of an elongated oval. Occasionall}' ver\' pe- 

 culiar irregular nuclei are found, antl one was seen whose 

 length was three times its width, without the aggregation of 

 chromatin to be described later, but with a clearly marked re- 

 ticulum and nuclear membrane. The nuclear membranes were 

 not shriveled or wrinkled in hardening, but are usually plump 

 and distinct, clear cut on their outer lines, and in almost all 

 ca.ses have taken a deep stain. 



The chromatin in these resting nuclei is disposed in a reticu- 

 lum that strongly reminds one of the bridles seen in the plant 

 cells. This reticulum is clearly continuous with the nuclear 

 membrane, as may be seen in very numerous instances, the 

 point of union of a strand and the nuclear megnbrane present- 

 ing a well-defined enlargement of the strand. In some nuclei 

 which hapi)ened to lie in the proper position, several of these 

 points of union in a single nucleus appear in the same plane, 

 giving the nuclear membrane the apjjearance of being toothed. 



Occasionally a nucleus is found in which all that is to be 

 seen within the nuclear membrane is this reticulum, without 

 local aggregations of the chromatin. In the greater number of 

 nuclei ihe chromatin is so disposed that certain local thicken- 

 ings may be observed. Under a power of about 500 diameters 



