The Nucleolus and Microchromosomes in the Spermatogenesis etc. 189 
The latter (although by its staining reaction and general be- 
haviour resembling a cbromosome whicb goes undivided to one pole 
in the Ist. naeiotic division) is really a uucleolus, disappearing enti- 
rely when tlie 2nd. meiotic prophase bas ended. There are 15 uni- 
valent cliromosomes in the 2nd. meiotic division. 
In both the Ist. and 2nd. meiotic divisions, there is a micro- 
chromosome, bivalent in the Ist. and univalent in the 2nd. In both 
cases, it lags behind the other chromosomes in division. 
Bibliography. 
1902. VoiNOV, C. R. Paris. Spennatogenese Cybister Roeselii. 
1903. Nils Holmgren, Auat. Anz. XXII. Spermatog. Silpha carinata. 
1905. E. B. Wilson, J. Exper. Zool. 
I. The Behaviour of the Idiochromosomes in the Hemiptera, p. 371. 
II. The paired Microchromosomes, Idiochromosomes, and Heterotropic 
Chromosomes in Hemiptera, p. 507. 
1906. III. Idem. The sexual differences of the Chromosome groups in 
Hemiptera etc. p. 1. 
1907. Biol. Bulletin. Vol. XII. p. 303. Note on the Chromosome groups of 
Metapodius & Banasa. 
1907. K. Foot & E. C. Strobell, The Chromosomes in Anasa tristis. Preli- 
minary note, Ibid. p. 119, & p. 279 — 316. 
Explanation of the Plates. 
All the drawings were made with a Zeiss 2 mm oil-imm., and 8 and 
18 oculars, and again considerably enlarged on paper. 
Plate IX. 
Figs. 1 to 7. Somatic division. 
Fig. 1. Resting spermatogonium. 
Fig. 2. Spireme just forming. 
Figs. 3 to 4. Further stages in the formation of the spireme. 
Figs. 5 & 6. Spireme breaking up, and formation of the chromosomes. 
Fig. 7. Somatic spindle. 
Fig. 8. Somatic telophase. 
Fig. 9. Early prophase of Ist. meiotic division. 
Fig. 10. Pairing of the chromosomes to form the gemini. 
Fig. 11. Earliest stage of the synapsis. 
Fig. 12. A slightly later stage than Fig. 11. Nucleolus (N) just distingui- 
shable. The archoplasm has almost entirely disappeared. 
