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Nachdruck verboten. 



The Accessory Chromosome in the Spider. 



A preliminary Notice by Louise B. Wallace. 



With 5 Fifjures. 



In the summer of 1899, at the Marine Biological Laboratory, 

 Wood's Holl, Mass., I began work on the spermatogenesis of the spider 

 under the direction of Dr. T. H. Montgomery and as some time will 

 elapse before the completion of the work, it seemed well to call 

 attention to one point which needs light thrown upon it by comparison 

 of many forms. The "chromosome nucleolus" (Montgomery) or "acces- 

 sory chromosome" (Mc Clung) has thus far been seen in the testicular 

 cells of Hemiptera, Coleoptera and Orthoptera but outside of the insects 

 it has not been reported, and it is a matter of interest to fiod out 

 how general is its occurrence in the Arthropoda. In the works of 

 Carnoy and Wagner, the only ones, so far as I know, who have written 

 on the spermatogenesis of the spider, I find no mention of any nuclear 

 element which might be taken for the accessory chromosome. Thus 

 far my work has been confined to an Agalenid, the testes being killed 

 in Flemming's fluid and stained with Hermann's stain. In this spider 

 the peculiar chromosome is conspicuous in the late spermatogouic 

 stages and in the prophase of the 

 first spermatocyte, its peripheral 

 position in the nucleus making it 

 easy to observe. Its origin in the 

 spermatogonia has not yet been 

 traced , but a gradual change of 

 form has been made out in the pig. i. Fig. 2 



early stages and, suffice it to say 



here, that in all of them it appears to be double. In Figs. 1 and 2 

 are shown cells in the prophase of the first spermatocyte, with the 

 double accessory chromosomes. 



In the monaster of the first spermatocyte the accessory chromo- 

 somes are easily distinguished from the others by their sharpness of 

 outline, slightly greater affinity for staining reagents and above all by 

 their eccentricity of position. They are always found on the periphery 

 of the spindle and often near the periphery of the cell. It is a cu- 

 rious fact that in the majority of cases both of these elements are 



