A STUDY OF CHROMOSOMES OF TOXOPNEUSTES 



VARIEGAT1 - WHICH SHO\\ IM >IYII>r.\l. 



!'i;< I LIARITIES OF FORM. 



BARBARA HEFFNER. 



INTRODUCTION. 



The observation- descril>ed in this paper were made during 

 tlic \\inter ami -priii;,;. 1909-10. in the Biological Lai > .rati ry 

 o| Br\n Maur ( 'ml< . Last Novemlnr after my arrival in 



Hr\n Ma\\r rp>tem I iinen t suggested to me a -tudy of the 

 hr"iu< tain echinoderms with -pecial tvl- 



in e to cl iliarities of form, a question e-|Hviall\ 



-unilic.ini since tlu- appearance of Baltxer's ('090) pa|*r mi llu- 

 <lii'in ..I > ntrotus livid us and Echinus ;: 



.\hiili h.i- thrown ne\\ li^ht on tie indi\ idnalit \ 

 "t i hn. in. hinoid-. I'revious to this author'^ lir-t 



publication mi tin- -nl.;-ii 'oHj there existed only a stigj;c-iimi 



!>\ lioM-ii 'ui .iml '1.7 i hat in some echinoids there occur chro- 

 mosomes "I a chai tic shajx.-. Baltxer pointed out that 



in l-.<i:inn \ ;;:.'- there are two very long rotl->hapcd 



chromosomes, t\\'' long hook-shaped ones, and two or thn-r 

 horseshoe-shaped chrmni-mnes, while in Strongylocentrotus livid us 

 then- are t\\o I .l--ha|>ed chromosomes, two long hok- 



-ha|)-l mil - and in a part of the eggs one smaller hook-shaped 

 chrmin'-i-ii.. \-> ihi- laiu-rone occurs only in a purl of tin- 



in al>mn mu- half "I them Baltxer suggests ('oga, p. 5 

 that it i^ ppiliai'!> an idi< x hromosome whose smaller matt- i- 

 1'iic of the ^horu-r P-d-~hai>ed chromosomes. The sanu- -ui;- 

 i"ii i- in. iili- in p-ard to one of the horseshoe-shaped chro- 

 nio-oiiH-- in /-., itinio. in cases \\hcre there are three of that t\pc. 

 \\'hile idiochromo-mm-> and other heterochromosonie- ha\e for 

 -mne ti.iie been kuo\\n in insects, arachnids and 



I t.ikr .nU.int j>|Mittiniiiy to express in; th.uiks i^r 



:."],ir>liip ,iu . M>I\\I .iii-l t<>r i-iu-nuranini; -uv;- 



and Dr. Su-vriis ihirin^ ill- i" my \vi>rk 



in their lalmiat^ 



