MATURATION PHENOMENA OF GERM CELLS. 145 



togenesis of some Hemiptera there is no rest stage in the growth 

 period of the spermatocytes, so that the chromosomes can be fol- 

 lowed from the spermatogonia to the spermatids. In Peripatus 

 this is but a short rest stage, and during it the boundaries of the 

 chromosomes can be readily distinguished. 



On the experimental side excellent evidence has been brought 

 in support of this view, particularly by the study of abnormalities, 

 by Boveri, l Zur Strassen, 2 Morgan, 3 and Herla. 4 



Evidence fully as strong as that from experimentaal study has 

 been obtained by observations upon certain modified chromo- 

 somes of insects, which are : 



3. THE HETEROCHROMOSOMES. 



I offer this name to include those peculiarly modified chromo- 

 somes to which have been given the names " accessory chromo- 

 somes " by McClung, 5 " small chromosomes " by Paulmier and 

 "chromatin nuceoli " by myself. They have been described for 

 the Hemiptera by Henking (/. c.), Paulmier, and myself; for the 

 Orthoptera by Wilcox, 7 McClung, Sutton, 8 cle Sinety ; 9 and for 

 the spider by Miss Wallace. 10 



1 "Zellen-Studien," Zoo/. Ja/irb., 1888 ; " Befruchtung," Ergcbn. Anat. Entw., 

 1891 ; " Ueber die Befruchtungs- und Entwickelungsfahigkeit kernloser Seeigel- 

 Eier," Arch. Enfwickmeck., 2, 1895 ; " Mehrpolige Mitosen als Mittel zur Ana- 

 lyse des Zellkerns," Verh. Phys. Ges. Wilrzburg, 35, 1902. 



2 " Ueber die Riesenbildung bei Ascaris-Eiern," Arch. Entwickmech., 7, 1898. 



3 " The Fertilization of Non-nucleated Fragments of Echinoderm Eggs," Arch. 

 Entwickmech., 2, 1895. 



4 "Etude des Variations de la Mitose Chez 1'Ascaride Megalocephale," Arch. 

 Bio/., 13, 1893. 



5 " A Peculiar Nuclear Element in the Male Reproductive Cells of Insects," 

 Zool. Bull., 1899; "The Spermatocyte Divisions of the Acrididre," Bull. Univ. 

 Kansas, 1900 ; " Notes on the Accessory Chromosome," Anat. Anz., 20, 1901 ; 

 " The Accessory Chromosome Sex Determinant ? " BIOL. BULL., 3, 1902 ; " The 

 Spermatocyte Divisions of the Locustidse," Kansas Univ. Sci. Bull., 1, 1902. 



" The Spermatogenesis of Anasa tristis," Journ. JMorph., 15, 1899. 



7 " Spermatogenesis of Caloptenus femur-rubrum and Cicada tibicen," Bull. Mus. 

 Coinp. Zool. Harvard, 27, 1895. 



8 " The Spermatogonial Divisions of Brachystola magna," Kansas Univ. Quar- 

 terly, 9, 1900 ; "On the Morphology of the Chromosome Group in Brachystola 

 magna," BlOL. BULL., 4, 1902. 



9 " Recherches sur la Biologic et 1' Anatomic des Phasmes," La Cellule, 19, 1901. 

 10 " The Accessory Chromosome in the Spider," Anat. Anz.,\%, 1900. 



