122 George Lefevre 



laterally curve backward and cross the corresponding rays of the 

 inner aster in the plane of the equator of the spindle, as in the 

 preceding figure. The chromosomes (tetrads), which show during 

 the prophases the varied forms described by Griffin, undergo a 

 concentration, and when seen in the equatorial plate present a 

 more or less uniform type consisting of a cross, with a pair of thick 

 broad arms in the equatorial plane and a pair of narrower perpen- 

 dicular arms. A split is frequently seen in the latter, and some- 

 times the transverse arms also appear to be divided in the middle 

 by a faint line. According to Griffin, the split in the transverse 

 arms of the cross corresponds to the original, longitudinal division 

 of the spireme segment, and the first maturation division is, there- 

 fore, equational or longitudinal. This may be the case, but after 

 a caretul examination of the tetrads in both unfertilized and fertil- 

 ized eggs, I am unable to find any definite basis for a determina- 

 tion of the character of the first division. The variability of the 

 form of the crosses renders the identification of either the equatorial 

 or the polar arms with the longitudinal axis of the primary rods 

 extremely uncertain. At the first mitosis, the crosses are drawn 

 out into ellipses, which then divide, the dyads passing to the poles 

 either as V's or double rods. The separation of the V's at the 

 apex takes place at the second maturation division, which Griffin 

 interprets as a reducing division. The outer pair of centrosomes and 

 group of dyads become contained in a small projection or knob of 

 clear, yolk-free cytoplasm, which by constriction around its base 

 is eventually cut oflF as the first polar body (Figs. 2i to 23). 



Before the close of the first mitosis, however, the two inner 

 centrosomes diverge in a direction nearly transverse to the axis of 

 the original spindle; a minute spindle appears between the two, 

 and around each centrosome a new system of delicate rays is 

 formed (Fig. 21). The dyads left in the egg lie at first on the outer 

 side of the spindle which now rapidly elongates and rotates through 

 about 90° of arc until it assumes a radial position with the outer 

 aster immediately under the point on the surface where the first 

 polar body was cut off (Fig. 22). The dyads, in the form of 

 double rods, arrange themselves in the equatorial plate with the 

 long axis across the spindle, as seen in the preceding figure, and 



