98 CHROMOSOMES IN THE SPERMATOGENESIS OF THE HEMIPTERA HETEROl'TERA. 



earlier one, heterochromosome, and etymologically has the same significance. Two main 

 kinds of allosomes are now known in spermatogenetic cycles, and these are : 



(a) Monosome {monosorna), an allosome that is unpaired in the spermatogonium, 

 i. e., without a correspondent mate there. Heretofore these have been named vari- 

 ously : accessory cJiromosomes (McClung), chromosomes spcciaux (de Sinety), chromosomes 

 X and impaired chroriiosom.es (Montgomery), heterotropic and differential chroTnusomes 

 (Wilson). 



(b) Diplosomc {diphsoma), allosomes that occur in pairs in the spermatogonium. 

 These have been previously denominated : small chromosomes (Paulmier), chrornaiin 

 nucleoli (Montgomery), idiochroviosomes and m-chromosovies (Wilson). 



I regret to have to add new names to the C3'tological dictionary, for there is 

 already somewhat of a chaos of them. But these seem to be about as simple and 

 uniform as could be invented, and I trust that their convenient brevity will insure 

 their adoption by fellow investigators. 



Wilson's recent series of " Studies on Chromosomes " has brought out two new 

 and important points with regard to the allosomes. One is that the diplosomes (his 

 idiochromosomes) of certain Hemiptera conjugate in the second spermatocytes and 

 there divide reductionally. This phenomenon had been entirely overlooked by me ; 

 my oversight was due in part to the fact that in most of the species I did not examine 

 the spermatogenesis beyond the stages of the first maturation mitosis ; and in greater 

 l)art to the fact that I was influenced by the thought that when there is an even 

 number of chromosomes in tlie spermatogonium there must be exactly half that 

 number of bivalent chromosomes in the first spermatocytes. And yet in certain 

 species (Enschishis tristigmms, Oncopclius, Zaitha), I showed that diplosomes may be 

 univalent in the first spermatocytes and divide there separately. Now I am able to 

 confirm Wilson's discovery for quite a number of species. His second and more 

 valuable conclusion is that when there is a single monosome in the spermatogenesis, 

 it is always represented by a pair in the ovogenesis ; and Miss Stevens and he have 

 enlarged upon this phenomenon to partially explain sex-determination. Further, 

 Wilson has found the occurrence of a monosome in certain Coreids where I had over- 

 looked it, and even in Anasa where his own student, Paulmier, had not found it. 



The present paper then is an attempt to reconcile these differences of observation, 

 on the basis of a fuller and more complete study of all of my old material. It 

 seemed clearest to present the facts gained for each species separately, then in conclu- 

 sion to bring them together under certain generalizations. 



The term "reduction division" is here used to express the separation of entire 

 chromosomes from each other in an anaphase of division ; or, in the case of a mono- 



