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Explanation of Plates. 
The individual photographs were taken as described on page 9. The three 
large negatives used for the reproductions were also prepared by us. Neither the nega- 
tives nor prints have been retouched in any way. All the photographs are of preparations 
made by our smear methods. 
Photos 1 — 54 were taken at a magnification of one thousand diameters, and 
photos 55 to 59 at a magnification of six hundred diameters. 
Plate II. 
Photo 1. Two first spermatocyte rest stages, each showing the two chromatin 
nucleoli tj'pical of this species. 
Photos 2 to 5. Five resting first spermatocytes, each showing the tj'pical two 
chromatin nucleoli, which are, as a rule, nearly equal in size. 
Photo 6. A resting first spermatocyte with 3 chromatin nucleoli, the two small 
ones together are about equal in size to the larger nucleolus. 
Photo 7. A resting first spermatocyte with the 2 chromatin nucleoli showing 
an unusual inequality in size. 
Photo 8. Nucleus of a resting first spermatocyte. The upper chiomatin nucleolus 
is breaking dowm into two unequal parts, indicating that this is the nucleolus from 
which the two idiochromosomes are developed, the lower chromatin nucleolus giving 
rise to a pair of the so-called ordinary chromosomes. 
Photos 9 to 10. Two resting first spermatocytes each with the characteristic 
two chromatin nucleoli. 
Photos 11 to 16. Six resting first spermatocytes in which there are three chro- 
matin nucleoli. In aU these cells the two smaUer nucleoli are together nearly equal 
in size to the large one. 
Photo 17. A resting first spermatocyte in which there are three chromatin 
nucleoli about equal in size. In this spermatocyte three pairs of chromosomes are 
probably being formed from the three chromatin nucleoU, instead of two pairs from 
two nucleoli. 
Photo 18. A resting first spermatocyte. In this preparation, one chromatin 
nucleolus appears to have given rise to the idiochromosomes, and the second cliromatin 
nucleolus has given rise to a pair of ordinary chromosomes. 
Photos 19 to 20. Four resting first spermatocytes, each one having the two 
tjqiical chromatin nucleoli. 
