March 20, 1908] 



SCIENCE 



445 



a typical sperm nucleus, while the tail 

 stains intensely and occupies a position 

 close beneath the vitelline membrane for 

 more than half the circumference of the 

 egg. 



A Contribution Towards an Experimental 

 Analysis of the Earyokinetic Figure: 

 Frank R. Lillie, University of Chicago. 

 (To be published in the proceedings of 

 the Central Branch.) 



The Accessory Chromosome of Anasa 



Tristis: Edmund B. Wilson, Columbia 



University. 



Certain contradictions in the literature 

 have led the author during the past year 

 to make an exhaustive re-examination of 

 the history of the accessory chromosome in 

 Anasa tristis, paying particular attention 

 to a comparison of sections, smears and 

 material in the unfixed, unstained condi- 

 tion. These various methods give thor- 

 oughly consistent results, which appear 

 with an elementary clearness that excludes 

 all obscurity of doubt. All the essential 

 facts in this species are as the author previ- 

 ously described them, and are uniformly 

 and consistently as follows: 



In Anasa tristis the fundamental somatic 

 number is in the male 21 and in the female 

 22. During the gi'owth period of the 

 spermatocytes the unpaired or accessory 

 chromosome retains the form of a con- 

 densed chromosome-nucleolus until the 

 early prophases of the first division. It 

 then elongates to form a longitudinally 

 split rod, again condenses to form the 

 eccentric chromosome of the first division, 

 and divides equationally in this division. 

 In the second division the grouping of the 

 chromosomes usually changes, and an ec- 

 centric position is no longer characteristic 

 of the odd chromosome. During the divi- 

 sion this chromosome passes undivided to 

 one pole, which receives eleven chromo- 

 somes, while the other pole receives ten. 



The spermatozoa are, therefore, of two 

 classes, equal in number; and comparison 

 of the male and female groups shows that 

 the eleven-chromosome class must be 

 female-producing, the ten-chromosome class 

 male-producing. These results have in the 

 meantime been independently confirmed by 

 a number of other cytologists. 



Abnormal Development of Frog Embryos 

 as a Result of Treatment of Ova and 

 Sperm with Roentgen Rays: J. H. Mc- 

 Gregor, Colimibia University. 

 Wood-frogs {Rana sylvatica) were taken 

 at the breeding season when about to dis- 

 charge the sexual products and exposed to 

 moderately strong Roentgen radiations for 

 periods varying from twenty minutes to 

 two hours, after which each one was 

 placed in a dish of water with a frog of 

 the other sex. In the series of experiments 

 were eases where both were exposed, and 

 others where only the male or only the 

 female was exposed. In all eases the frogs 

 paired promptly and all the females de- 

 posited eggs. 



The study of the development of the 

 eggs yielded some interesting results, which 

 may be stated in very general terms as 

 follows: Where only the female was ex- 

 posed, the male being normal, all the eggs 

 developed, about 5 per cent, of them de- 

 veloping various abnormalities. Where 

 the female was normal, the male only ex- 

 posed; only about 5 per cent, of the eggs 

 were fertilized and of these the majority 

 developed various deformities during early 

 stages. Wlien both were exposed the re- 

 sult was practically the same as when the 

 male alone was treated. 



The deformities were of various types, 

 among which may be noted bladder-like 

 distension of ccslom, tumor-like prolifera- 

 tions on various parts of the body, double 

 tails, and atrophy of certain parts of the 

 brain. Of two larvas which lived five 



