322 



ROBERT W. HEGNER. 



OOC 



of January, 1908, a number of copepods was found scattered 

 about in the vegetation which was gathered from the rocks on 

 the bottom of Lake Monona, Madison, Wisconsin. These were 

 identified as Canthocamptus staphylinus Jur. 1 I sectioned some 

 of them and found a number of oocytes 

 in process of division. A few of these 

 contained mitotic figures which possessed 

 distinct polar rays at either end of the 

 spindle, and were entirely enclosed within 

 the nuclear membrane. This, I believe, 

 is the first instance on record of such a 

 phenomenon in the cells of either plants 

 or animals. 



The ovaries of CantJwcamptus lie in 

 the dorsal cephalic region. The two ovi- 

 ducts extend posteriorly from them lying 

 on either side of the median line of the 

 body ; each when filled contains a single 

 row of eggs. The primary oocytes can 

 readily be distinguished from the grow- 

 ing oocytes by the different staining 



Partially diagram- adt of thdr lk kden cyt oplasm. 



rig of a longitudinal 



In the case of the latter the cytoplasm 

 ducts of Canthocamptus staphy- stains very deeply in hematoxylin, while 



linus Jur. a, oocyte shown that of the eggs j n the processes Q f ma _ 



enlarged in Fig. 2; o'o, growing . 



oocytes; ode, primary oocytes, turation IS much less Susceptible to this 



dye. An abrupt change in the chemical 

 character of the cell contents may thus be recognized where the 

 growing oocytes end and the primary oocytes begin (Fig. 1). 



In the present paper we shall consider only the primary oocytes 

 in the equatorial plate stage of nuclear division. Several hundred 

 females of Canthocamptus were sectioned, but only two of these 

 contained eggs showing mitotic figures. Twenty-two of the eggs 

 examined were in process of division ; in each one, the entire 

 amphiaster was found within the nuclear membrane. One of these 

 eggs (Fig. 1, a) is shown enlarged in Fig. 2. The chromosomes 

 have been drawn up about the spindle and form the equatorial 



1 I wish to thank Mr. C. Dwight Marsh for determining the species for me. 



Fig. 1. 



matic drawing of a longitudinal 

 section through the two ovi- 





