686 EEPORT— 1901. 



1st. The rings are drawn out on the spindle, and break into V-shaped daughter 

 chromosomes. 



In the anaphase in .9ome rases each daughter V is found again divided into 

 two V's» and the scnondary cleavage is held tn be longitudinal. In other eases 

 the V's break at their apices into double rods by a cleavage held to be transverse. 

 No solution of this contradiction is found along this line. 



ynd. The rings are doubled up on themselves and are resolved by being 

 reopened along the plane of the bend. There is a second longitudinal cleavage 

 seen, but it is only aj'pai'ent. Variation in the form of the chromosomes is 

 explained by variation in the degree of the cleavage, by variation in the insertion 

 of the traction fibres, and by different degrees of bending of the rings (Farmer and 

 Moore). 



?>vA. There is a real second longitudinal cleavage which appears in the 

 metaphase, and is completed in the anaphase of the first Jlitosis. Thus daughter 

 and granddaughter chromosomes are formed in the course of the first Mitosis, the 

 second Mitosis merely distriljuting the granddaughter chromosomes (Gregoire, 

 8trasburger, 1900). 



This view of the heterotype serves in Strasburger's latest work to explain all 

 the phenomena in plants — difterences arising only from the manner in which the 

 double rod prophase figures are placed on the spindle. In the animal series only 

 Carnoy and Le P.run and Janssens adopt the idea of the simultaneous double 

 longitudinal cleavage in Triton. 



When true tetrads occur the first Mitosis is not strictly heterotypical in 

 character. In recent studies of the phases in Echinus I have found typical 

 tetradal bodies, never rings, yet the first Mitosis is heterotypical in character, and 

 my results show that part at least of the problem of reduction lies nut, as has been 

 held, in the determination of the on'i/in, but rather in the fate of the tetrads. 



Thus in Echinus esculentus there are sixteen tetrads, each consisting of a pair of 

 slightly curved bilobed rods lying back to back. The tetrads come to lie radially 

 on the first polar spindle. Each is opened out like a hinge from within outwards, 

 while at the same time a second longitudinal cleavage is taking place from without 

 inwards. Lozenge-.shaped figures are produced : these elongate greatly and 

 ultimately break at the equator into two V's, which again in the anaphase break 

 at their apex to form two short bilobed rods lying back to back. This apical 

 splitting is the completion of the second longitudinal splitting. These bilobed 

 rods pass unchanged into the second Mitosis, arrange themselves radially on the 

 spindle, are opened out and separated Jrom one another as the granddaughter 

 chromosomes, formed in the anaphase of the 1st Mitosis by the second longitudinal 

 cleavage. In the second polar body each remains as a short bilobed rod, but in 

 the ovum each greatly elongates into a sharply bent V- This change in the size 

 of the chromosomes is important as indicating the relaxation from the very con- 

 densed condition of the chromatin rods characteristic of the divisions with the 

 reduced number of chromosomes. 



Applying the hypothesis of ' Pseudo-reduction ' (Hiicker and Riickert) to the 

 facts observed each half of the tetrad might be considered to represent two 

 chromosomes united end to end by the omission of the last segmentation of the 

 chromatin thread. 1'hrough all the phases the fate of each lobe or sphere of the 

 tetradal body can be traced. The tacts can be expressed in the usual formula, 

 thus, for each of the sixteen tetrads : — 



l.^t Mitosis. 



/ I A A A 



b b 



a) I i (2) a (3) a (4) .^ (r.) 

 )j b 



