626 DR A. ANSTRUTHER LAWSON ON 
Fig. 21. Another stage of the same. 
Fig. 22. The same. This and the two preceding figs. show clearly that as the pairing of the univalent 
chromosomes becomes more intimate, the bivalent structure becomes very much shorter. This is mainly 
due to the shortening and thickening of the two uniting elements, but also partly due to the coiling of these — 
structures about one another. 
Fig. 23. The bivalent chromosomes are now almost completely organised. 
Fig. 24. The bivalent chromosomes now occupy a position at the periphery of the nuclear cavity—the 
majority of them being in close touch with the nuclear membrane. From this and the preceding figures it 
will also be seen that the bivalent chromosomes are heteromorphic. There are long ones and short ones, 
Fig. 25. An early stage in the formation of the spindle. The nuclear vacuole shows a very marked 
decrease in size. Accompanying this decrease fine delicate threads of cytoplasm appear about the nuclear 
membrane, which still remains intact. 
Figs. 26 and 27. More highly magnified details showing the manner in which the univalent chromosomes 
coil about one another in the process of pairing. 
Fig. 28. Another stage in the formation of the achromatic figure. The nuclear membrane is intact and 
quite evident, and the karyolymph has become very much reduced. The number of cytoplasmic threads has 
correspondingly increased, and we have a typical multipolar spindle. 
Fig. 29. A further advanced condition of the same. The karyolymph is so much reduced that the nuclear 
membrane is 1n touch with the chromosomes, which have become crowded together. 
Fig. 30. The same still later. The nuclear membrane being now in intimate touch with the chromosomes 
is no longer visible. Up to this stage there was no evidence to show that the nuclear membrane had broken 
down. , 
Fig. 31. The mature achromatic figure with the bivalent chromosomes in their characteristic position at 
the equator. 
Fig. 32. The same at a later stage, showing the separation of the chromosomes. 
Fig. 33. A section showing a polar view of the chromosomes at the equator. The long and short 
chromosomes may easily be seen. 
Fig. 34. The chromosomes on the way to the poles. 
Fig. 35. A polar view of the same. 
Fig. 36. The chromosomes at the poles. 
Fig. 37. The chromosomes have passed beyond the region of the poles of the spindle, and are becoming 
grouped together in two masses at opposite ends of the cell. Numerous drawn-out threads of cytoplasm 
stretch between the two masses. : 
Fig. 38. A slightly later stage of the same. 
Fig. 39. The chromosomes have become vacuolated by the accumulation of karyolymph, and a plasmatie 
membrane envelops each daughter nucleus. 
Fig. 40. The daughter nuclei at a later stage. A cell membrane has been laid down midway between the 
daughter nuclei. As the nuclear vacuoles enlarge the cytoplasmic threads stretching between them vanish. 
Fig. 41. A spindle of the second meiotic division with the chromosomes passing to the poles, This 
figure also shows the enormous thickening of the cell-wall. 
Fig. 42. The same, with the chromosomes at the poles of the spindle. 
Fig. 43. The result of the second meiotic division showing three of the four spores enclosed within the 
common thick mother membrane. 
Fig. 44. A section of a microspore after the absorption of the mother-wall and the separation of the 
tetrads, The chromatin has again become very finely divided in the so-called reticulum stage. 
Fig. 45. A section of a mother-cell of Kniphofia. The chromatin is in the form of spireme threads 
which show the longitudinal fission. 
Fig. 46. The same at a little later stage. 
Fig. 47. The same, showing the lateral pairing of the thickened spiremes to form the bivalent 
chromosomes. 
Fig. 48. The same, showing the tight coiling of the pairing chromosomes. 
Fig. 49. Another example of the same. 
