THE GERMINAL SPOT IN ECHINODERM EGGS. 



BY H. E. JORDAN. 



The object of this paper is to report the results of further studies of the 

 prematuration stages of echinoderm eggs. The main problem involved is 

 to determine the relation of the nucleolus to the chromosomes during the 

 growth-period. I have recently shown that in both Asterias forbesii and 

 Hipponoc esculcnta the chromosomes for the first maturation mitosis arise 

 from the nuclear reticulum with some variation of details in the two species. 1 

 In Asterias forbesii the chromosomes subsequent to origin assume a more 

 or less intimate connection with the nucleolus just prior to maturation, and 

 the nucleolus, after passing through a preliminary process of fragmenta- 

 tion, apparently contributes chromatic material to the chromosomes. In 

 Hipponoe esculenta the relationship between nucleoli and chromosomes if 

 indeed one exist at all is more obscure, but the nucleoli here also disappear 

 about the time of maturation. The ultimate aim of these studies is to obtain 

 some information regarding the function of the germinal spot. 



1 am now able to report upon two additional species of echinoderms, 

 one again a star-fish (EcJiinaster crassispina) and the other a brittle-star 

 (Ophiocoma puniila}. The latter appears to agree rather closely with what 

 obtains in Hipponoc and with what Wilson 2 reports of some of the sets 

 of eggs of Toxopneustes variegatus treated with MgCl, ; while Echinaster 

 presents a case unique in that the chromosomes here appear to arise as the 

 direct products of nucleolar fragmentation. I regret that my material does 

 not yield stages for the study of either the oogonial history or the matura- 

 tion mitoses, but the various stages of the growth-period, which are repre- 

 sented in great variety and abundance, give conclusive results in regard to 

 the essential point, i. e., the origin of the chromosomes. I trust the com- 

 ing summer will yield the stages desired for a more complete study of the 

 oogenesis of these highly interesting forms. 



The material at my disposal was collected during a brief stay at the 

 Marine Biological Laboratory of the Carnegie Institution of Washington, 



Jordan, H. E., 1908. The relation of the nucleolus to the chromosomes in the 

 primary oocyte of Asterias forbesii. This volume, p. 39. 



2 Wilson, E. B., 1901. A cytological study of artificial parthenogenesis in sea- 

 urchin eggs. Arch. Entwickl., Mech. Bd. 12 : 529. 



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