1905.] NATURAL SCIENCES OF PHILADELPHIA. 193 



in pairs in the spermatogonia, I was able to determine the following 

 relations (1901). In all the species of Hemiptera these imite to form 

 one bivalent chromosome in the first spermatocytes, which appears 

 clearly double at the time of the first maturation mitosis. In Euchistus 

 variolarius, Hormostes, Protenor and CEdayicola the heterochromosomes 

 of this type divide rcductionally in the first mitosis, so that their uni- 

 valent components become separated; in the second mitosis each 

 divides again, by comparison with the other chromosomes probably 

 equationally, though I could not determine this in any decisive manner. 

 The same process Gross (1904) has described for the chromatin nucleoli 

 of Syromastes, and I have recently found it to hold for Euchistus tristig- 

 mus.^ For Anasa tristis, Alydus eurinus, Corizus, Oncopeltus, Calocoris, 

 Acholla and Zaitha I found (1901a) the bivalent heterochromosome 

 to divide reductionally in the first mitosis, but did not determine its 

 behavior in the second; this is also the case in Lygus, Nobis, Corizus, 

 as I showed in the supplementary paper (1901&). Paulmier (1899) 

 found the bivalent heterochromosome of Anasa to divide reductionally 

 in the first mitosis, but not to divide in the second, in agreement with 

 Henking's (1890) observations on Pyrrhocoris, and with those of IMcGill 

 (1904) on Anax. That the bivalent heterochromosomes of Syrhula 

 and Lycosa probably, but not certainly, divide first reductionally, then 

 equationally, in the two maturation mitoses is shown in the present 

 paper. Finally McClung (1900) describes for Hippiscvs an accessory 

 chromosome of the spermatocyte, said to divide in both maturation 

 mitoses; he does not describe the relations for the spermatogonia, but 

 it is quite probable to my mind that the phenomena in Hippiscus will 

 be found essentially similar to those determined by me for Syrhula, 

 namely, a bivalent heterochromosome in the first spermatocyte, 

 formed by the conjugation of two univalent heterochromosomes of 

 the spermatogonium. 



We can summarize the facts of the preceding paragraph, noting 

 parenthetically that for the details in the various species the reader 

 must refer to the original descriptions, in the following statement: 

 when heterochromosomes occur in pairs in the spermatogonia, i.e., 

 are of the type of " chromatin nucleoli," they always unite by conjuga- 



^ On a renewed study of my old preparations of the last species I find this to 

 be certainly the case, and my earher statement (1901a) was erroneous, to the 

 effect that "the bivalent heterochromosome divides first equationally, then reduc- 

 tionally. Also in my account of E. variolarius (19016) I stated the heterochromo- 

 some in the second mitosis "is not always divided"; that must be amended to 

 read "seems not always to be divided," in that in some of the spermatids it escapes 

 detection by its small size or by being covered by another chromosome. 



13 



