198 



Dr. L. Doncaster. Gametogenesis and 



DESCRIPTION OF FIGURES. 



The figures are all freehand, drawings made with a Zeiss 2 - 5 mm. immersion lens 

 (N.A. 1'40), and compensating ocular 12. They are not all exactly on the same scale. 

 In many of the figures, especially those representing the earlier stages of the maturation 

 divisions {e.g., Series IX), the difficulty of interpreting and representing the structures 

 in perspective with complete accuracy has proved insuperable, and the figures must 

 therefore be taken as giving as close a rendering as I am able to do of the appearance 

 presented, rather than as drawings which are accurate in every detail. In each case the 

 line on the left of the figure represents the position of the egg-margin. The Roman 

 numerals represent (except in Nos. IX and X) different individual females, so that, for 

 example, Figs. VII, 1-8, represent eight maturation figures from eggs laid by one 

 parent. Series IX and X represent figures at various stages of division from eggs of 

 mixed females ; of these, Figs. IX, 1-6, and X, 3 and 5, were preserved in 1907 ; X, 1, in 

 1906 ; X, 4, in 1914, and X, 2, in 1915. All, the eggs of Series I-VIII were preserved in 

 1914 or 1915. 



Series I, 1, 2. — "Top-shaped'' type of nucleus just before maturation. In I, 2, the 

 stained granules, suggesting emission of chromatin, are seen round the 

 equator. 



I, 3- — Early stage of division ; since in some cases the chromosomes are 



lying one directly over another not all are shown. 

 I, 4. — Later stage of division. The inner group has divided into egg-nucleus 

 and inner polar group ; the outer group has not yet divided. The figure is 

 reconstructed from four successive sections. 

 Series II, 1 and 2. — Top-shaped nuclei with double rings of granules. 



II, 3. — Prophase with narrow loops or strands becoming drawn out on the 

 inner side. 



II, 4. — Unusually regular division-figure. The inner and outer groups are in 

 successive sections, with the exception of the chromosome marked x in the 

 outer group, which is in the same section as the inner group. On the inner 

 side of the inner group 10 spindle-fibres can be counted with some 

 confidence. 



II, 5. — Three groups of polar chromosomes after the completion of the matura- 

 tion divisions. The lowest and that near the edge are the halves of the 

 outer group and are in one section ; the upper on the right hand is the 

 inner group containing 10 chromosomes, and is in the next section. 

 Series III, 1, 2, 3. — Prophases ; III, 1, has the typical top-shaped form with equatorial 

 granules. 



Ill, 4. — Chromatin strands being drawn out on both inner and outer sides. 



Owing to superposition and perspective, not quite everything is shown. 

 Ill, 5, 6. — Two double division figures, on rather a larger scale than the 



remainder. In each case the outer group is in one section, the inner in the 



next. 



Ill, 7. — Completion of maturation division and sperm-head (Sp.) swelling up to 

 form male pronucleus. The two outer groups of polar chromosomes (the 

 outermost with about 10) and the inner group are in one section, with the 

 exception of the chromosomes represented separately below, which are in 

 the next. The egg- and sperm-nuclei (marked 5 and Sp.) are both in the 

 next section but one. 



