A STUDY OF THE CHROMOSOMES ( )F HIPPONoE 

 ESCULENTA AND MOIRA ATROPOS. 



EDITH IMXXI \ 



Tlir comparatively recent investigations made <>n fertili/ed 

 echinoderm ci;i;s with especial regard to the qneMion of chromo- 

 some individuality had their beginning in an attempt to correlate 

 the behavior of the chromos, >nics during fertilisation and the 

 subsequent cleavage stages with the observed facts of parental 

 dominance in hybrid cultures. 



The first observations are recorded by Tennent, '07. He 

 the equatorial plates of Toxopueustes runt'^iti's, Moini 

 and Arbacia pitnctnlata in which individual characteristic- 

 for each species are evident. The contrast between the chromo- 

 some L^roups in Moini and Arbacia is so apparent that in the 



A rbacia cf 



equatorial plates of the hybrid the hybrid nature of 



Moira 9 



the -e-inentaiion nucleus is e.isily reco.u'iii/ed. 



Baltzer, '09, in an e\ti-n>i\-e morphological Mudy of the chro- 

 mosomes of the European forms, Strongylocentrotus Uridiis and 

 microtuberculatus, was able to identif\- single chronio- 



Strongylocen- 



s which could be recognized in the hybrid 



j he Inn us 9 



The main facts which he describe^ ma\- for the sake 

 o] comparison be brielly stated at this point. 



The chromo-omrs of Strongylocentrotus are in general rod- 

 -haped bodies which \ai~\- in length. The longest are Over three 

 times | he length of the shorteM. In addition to the>e then- are 

 in one-half of the e^> i \\ o and in the other half, three hook- 

 shaped elements. The occasional third hook is smaller than tin- 

 other two which are equal in sj/ r and evidently form a somatic 



1 Bovcri in hi- " /.<-V<-\\ stinli.-ii." lint VI., \<>-. Jena. ra!li-l aticntion to 

 Baltzer's observation- uhirh weir licin inalf al iliai lime in Mn\ n i'-, la I >< <i ai >i y. 

 Ho publishes oni' fiKun- ni Stt iitrotit* -hd\\-in- a linnk-'-li.i|ii-il c hn iiim-i unc. 



He himself in 1890 ha<l iininl tin- m-i uiiciu < i.| rods "I ililii-n-nt lrni;tli> in certain 

 echinoderms. 



1 68 



