668 



THE AMERICAN NATURALIST 



[Vol. XLI 



illustrating the nature of heterotypical mitosis and showing that its 

 significance in reduction divisions has been overestimated. Hetero- 

 typical chromosomes were demonstrated in the first cleavage division 

 of Nereis. In the second maturation division of Amphiuma and in the 

 first cleavage of Thalassema, cross-shaped chromosomes were shown. 

 Cross-shaped chromosomes or tetrads are therefore not limited in Tha- 

 lassema to the first reduction division. The tetrad shape was shown 

 in some of the chromosomes of Nereis in metaphase fifteen hours after 

 fertilization. A longitudinal splitting of the daughter chromosomes 

 was shown in a cleavage mitosis of Nereis and also in its second matu- 

 ration mitosis. Other features of chromosome structure which were 

 demonstrated, include the spiral coiling of chromosomes in Amphiuma 

 and Ascaris, and a spiral chromatic thread w^ound around the surface 

 of each chromosome in the root tip of Allium. The relation of chro- 

 mosomes to the resting nucleus was illustrated, and new chromosomes 

 were said to arise within the disseminated chromatic material of the 

 old ones. 



Miss A. M. Lutz of Cold Spring Harbor showed sections of the root 

 tips of Oenothera lamarckiana, its mutants and hybrids, to (ieinoii- 

 strate the variations in the number of somatic chromosomes. The 

 material appears very favorable for the counting of ( liroiiiosoiiics, 

 and it was remarkably well preserved and clearly stained. Never- 

 theless the question of one chromosome more or less in a given count 

 is sometimes very difficult to determine. To the counts which have 

 been made and were demonstrated by Miss Lutz, those recently 

 published by H. K. C.-.tes from s„niiilii- e(>lls of the flowers may be 

 added; their counts ;ire ;is follows, Oniothera lamarckiana, pure 



the number is ever higher," (iates); (). (/if/a.s\ L'S with ;i stiiri^estion 



that gifjas has double that number, suggesting a variety like A.scaris- 



