A HETEROCHROMOSOME OF MAI.F oRIC.IX 



i\ la -in \oins. 



MAVII) HII.T TKXXhX i 



The observations of Haltzer ('09) seem in have led to an 

 immediate conclusion that in cchinoid^ the female is the hetero- 

 gameticsex while tin- male is homogametic. My observations on 



Illpponnc cf 1 



the - cross, taken in conjunction with those of Heff- 



1 oxopneustes 9 



HIT MO) and Pinney I'll) show that this conclusion cannot be 

 final. The study of the material mentioned has given con- 

 vincing evidence that in Jlippouoe cscnloita (Tripneustes esciilen- 

 ///M.a heterochromosome is carried by half of the spermatozoa 

 and that the dimorphism of somatic chromosome groups in 



Uipponoe cf 



in straight tertih/ed Inpponoi 'and ,., material must 



1 oxopneustes 9 



be i orrelated with dimorphism of the spermatozoa. 



The heterochromosome in question is hook-shaped in form 

 // Fi^. i, A, H Fig. 2, B). In a study of fifty- two spindles in 



A B C 



i. Tuxnfim-H.^lfs 9 X IIif>{xie c? 'I'lncr 1< >ni;ii ii'linal sections oi 

 spirull'- in anap!ia-c. In A and /-' twi. chnniK. ;t in i.utliin- ii.r -ak. .-I 



\ t, ( lllnlllri-i.llli - -ll'.UIl. lli.uk- ill -iili- \ic\V. XI..S" 



which 1 ua> able to reach a definite conclusion a- to tin- pre-ence 

 or absence of the hook-shaped element , it \va> found to be present 



in twenty-eight and absenl in twenty-four instances (Fi^. ^ ! - 



Miss Pinncy ('iu has been abK' to sho\\- the occurrence "t 

 this element in half of the straight I'eriili/ed llipfxnn' The 



152 



