142 Chromosomes in the spermatogenesis of the hemiptera heteroptera. 



(19056) finds the monosome to disintegrate in the second spermatocyte l>ut to probably 

 reappear in the spermatids ; and in Feriplaneta where iMoore and Robinson (1905) con- 

 clude there is no allosonie, but reinvestigation of tliis species is needed because Miss 

 Stevens has described a monosome in the closely related Blattella. McGill (1901) has 

 described for Anax, an Odonate, an allosome that divides in the first maturation mitosis 

 and not in the second ; but this author identifies this single element with a pair of chro- 

 mosomes of the spermatogonium, which makes the phenoniena somewhat difficult to 

 interpret. The account of the spermatogenesis of the coleopteron Cybistcs, given by 

 Voinov (1903), I have not seen. Miss Stevens (1905/^) finds them to be absent in 

 aphids and Termopsis (a termite) ; in the coleopteron Tcnchrio she describes a pair of 

 very unequal diplosomes that divide in the maturation mitoses first reductionally and 

 then equationally ; and in Sagitta she describes an allosome that divides in both matu- 

 ration divisions. In Agalena Miss Wallace (1905) finds a pair of diplosomes that do 

 not divide in either maturation mitosis, which is quite different from my own results 

 upon Li/cosa (1905), to the effect that the pair of diplosomes divide reductionally and 

 then equationally. The spermatogenesis of the Chilopods [Scolopendra), as described 

 by Blackman (1905a, 6), is peculiar in that the monosome during the growth period 

 comes to contain all the autosomes, so to form a " karyosphere "; they pass out of it 

 before the first maturation mitosis, where it does not divide, but it divides equationally 

 in the second mitosis; essentially similar results were obtained by Miss Medes (1905) 

 for ScvAigera. Some of the most interesting and complex relations of monosomes have 

 recently been found by McClung (1905) in various acridiids, consisting in the adhesion 

 of the monosome to one or more autosomes whereby plurivalent elements may be 

 formed not only in the spermatocytes but even in the spermatogonia. 



We may now attempt to decide what decisions tlie diversity of behavior of the 

 allosomes, particularly in the Hemiptera, may give in regard to their genesis and 

 mutual relations. 



Since Henking's first discovery of tliem in Pyrrhocorls all observers have been 

 in agreement that they are modified chromosomes. And on the observational basis 

 that we have today we ai-e in position to conclude wluit this genesis may have been. 

 In the first place the ordinary chromosomes, the autosomes, of the Hemiptera are 

 proven to divide in the maturation mitoses first reductionall}^ and second equation- 

 ally. The results of Henking, Paulmier, Stevens and myself are in agreement on tliis 

 issue, and only Gross assumes a reversed order of division ; Gross's position is not 

 borne out by his own observations, as I pointed out in another place (1905) and there 

 reasoned, and Gregoire (1905) has strongly seconded me in this, that probably in all 

 Metazoa the first maturation division is reductional and the second equational. On 



