Spermatogenesis in spider. 557 



2. The Accessory Chromosome of spiders. 



The origin of the accessory chromosome has been determined 

 for only one spider in the present study and since the evidence 

 has already been given there is no need of repeating it here. 



The fact that the accessory chromosome elements may appear as 

 separate chromosomes during the spermatogonial division is not 

 peculiar to spiders. Gross (1904), showed that the accessory elements 

 of Syromastes marginatiis came from two spermatogonial chromosomes 

 and his work was later confirmed by Wilson (Study IV) who 

 showed also that the female carried two measures of the accessory 

 bodies. Essentially the same thing was found by Morgan in the 

 case of Phylloxera fallax; by Payne in some of the Reduvioids (1909), 

 and by Edwards (1910), in Ascaris lumhricoides. 



No Y- element has been found in any of the 13 families of 

 spiders studied up to the present time. In every case the accessor}^ 

 chromosome is made up of X-elements, the two rods lying side by 

 side during the maturation period and acting as a single body; see 

 Figs. 5, 38, 54, 65, 71, 85, 87, 92, 94, 98, 112, 115 and 117. The 

 accessory elements pass undivided to one pole and as a result, part 

 of the second spermatocytes carry them and part lack them. In 

 the second division when the accessory chromosome is present 

 it divides. Thus the sperm are dimorphic as regards this bodj^, 

 one half of them carrying the accessory chromosome and half 

 lacking them. 



It must be evident that while the accessory chromosome may 

 arise from two spermatogonial chromosomes, it behaves during the 

 maturation divisions as a single element and that the type of 

 distribution, which we find among spiders, is the same as that found 

 in Anasa irisHs and other like forms as described by Wilson. 



This constant behavior and appearance of the accessory chromo- 

 some in the various families of spiders, including the most primitive 

 forms studied as well as the highly specialized families, is very 

 suggestive. Recent palaeontological works on spiders, especially a 

 monograph by Pocock (1910), have shown that even in very early 

 geological periods we have highly specialized families such as the 

 Argiopidae. And it does not seem improbable, indeed we may say 

 with certainty, that many of the families which we know today 

 sprang from the parent stem very early and have existed in much 

 their present form for millions of j^ears. It is a very interesting 



ZooL Jahib. XXXVIIL Abt. f. Anat. .87 



