526 The Ohio Naturalist. [Vol. VI, No. 7, 



Fig. 5. A continuous spireni singly split. The spirem may be 

 traced bv focusing from the granules at the right around the elbow above 

 and back on the left side where after crossing twice it turns and passes 

 under the elbow to the granule next the starting point. In addition to 

 this there can be traced from the first granule, a loop passing under the 

 other large granules where its relations cannot be made out. It is not 

 impossible that this loop is not linin at all but some cytoplasmic conden- 

 sation. It is not like the rest of the spirem in appearance. On sui.erfi- 

 cial examination the right portion might be mistaken for an end view of 

 a tetrad with bridges between the rods but its relations to the whole 

 clearly negate any such possibility. 



Fig. 6. A split spirem doubled on itself to form the two tetrads. 

 It has already broken apart at the upper end of the right tetrad leaving 

 two loose ends, connected by a faint strand of dense sytoplasm. 



Fig. 7. Spirem in which one strand is twisted entirely around the 

 other in a manner impossible in a split rod. The two ends of the loops 

 are beginning to break apart or perhaps have already broken but remain 

 in close contact. 



Fig. 8. One tetrad nearly formed, the other lagging. The relations 

 of the four rods to the right are not possible to make out precisely. On 

 the left the loop of the original spirem is still evident: This shows the 

 longitudinal split faintly in the distal end. Such a figure as this might 

 easily be interpreted as due to a double split. The loop looks at first 

 sight like the incompletely separated ends of a longitudinal split. But 

 at the point of junction the distal (left) arm turns up and then bends 

 down to meet the other which in like inanner turns down and then up 

 making a rounded loop perpendicular to the plane of the paper. One 

 arm of the loop is also much shorter than the other but dees not seem to 

 be cut off or disturbed. 



Fig. 9. A nvicleus in which one of the two tetrads is much more com- 

 pletely formed than the other. The right tetrad is seen to be composed of 

 four rods two above the others. The spirem has completely broken across 

 between the two arms of the loop and in one side the longitudinal split 

 is also complete while in the other there remains a bridge across between 

 the two portions. At the base of this tetrad both arms are seen to be 

 continuous with the spirem which starting from one arm bends around and 

 is twisted on itself in the position of the left tetrad, returning to the 

 second arm of the right tetrad. In the parallel strands near the right 

 tetrad are seen two pairs of small granules which may be chromatin or 

 merely thickenings of the linin thread. Were it not for the evidence of 

 the rest of the loop these might be taken to have arisen by a longitudinal 

 split but such an interpretation is clearly impossible of the twisted spirem 

 of which they are a part. 



Fig. 10. A continuous split spirem of almost the same age as figure 

 6, in which the tetrads are clearly forshadowed though not yet differen- 

 tiated. Contraction with conseojuent obliteration of the chromatin gran- 

 ules has gone further than in fig. 6, but the arm of the tt^rtads have not 

 approached closely nor has any break occurred. The linin connections 

 which are very evident were largely lest in repn duction. 



Fig. 11. A nucleus in which the four chromatids of each tetrad are 

 clearly visible. The double linin thread may be traced into the overlying 

 chromatids of the right tetrad which bend back and down to become con- 

 tinuous with the two underlying chromatids which in turn are contin- 

 uous with the second pair of strands of linin tliread. The connections 

 of the left tterad with these linin threads is so indistinct as not to be exactly 

 traceable. The left tetrad is in such a position that three of its chroma- 

 tids are visbile while the fourth may be traced by focusing down. The 

 difYerent chn^matids are much connected V)y bridges. 



Fig. 12. A pair of tetrads fully formed anol lying in tlie maturation 

 spindle, showing the characteristic angle between them. 



