EXPLANATION OF PLATES 



All of the figures are reproduced directly from photographs by the author, without retouching. The 

 originals were taken with a Spencer -fa oil-immersion, Zeiss ocular 6, which gives an enlargement of 1500 

 diameters. The admirable method of focusing devised by Foot and Strobell was employed. They 

 are reproduced at the same magnification. 



PLATE I 



(Photos i to 5, 10 to 23, Syromastes marginatus; 6 to 10, Metapodius terminalis; 24 and 25, Pyrro- 

 choris apterus). 



i and 2. Spermatogonial groups of Syromastes; copied in Text-fig, i, a, b. 



3 to 5. Polar views, first maturation metaphase; w-chromosome at the center, idiochromosome- 

 bivalent ("accessory" chromosome) outside the ring at the left. 



6 and 7. Corresponding views of Metapodius, typical condition with the two separate idiochromo- 

 somes outside the ring at the left. 



8 and 9. The same; exceptional condition, with the idiochromosomes (at the left) in contact. 



10. Polar metaphase, second division, Syromastes. 



II to 17. Side views of the same division. The duality of the idiochromosome appears in 12, 16 

 and 17. 



18 to 23. Early prophases of first maturation division, Syromastes. Each of these shows the 

 separate wz-chromosomes, and in all but No. 20 the chromosome nucleolus (idiochromosome bivalent) 

 also appears. 



24 and 25. Spermatogonial metaphases of Pyrrochoris (copied in Text-figs. 2, a, i). 



