112 



Gametogenesis of the Gall-Fly, etc. 



Fig. 18 a, h. — Two prophases from a probably abnormal follicle. In 18 a the double 

 number of chromosomes is seen, in 18 6 they appear to be pairing 

 longitudinally. In 18 6 not all the chromosomes are shown. 



Fig. 19 a, h. — Anaphases from mitoses in ovary of half-grown female larva, summer 

 generation, a, polar view ; 6, side view. 



Fig. 20. — Part of egg tube fi-om pupa of summer generation, showing alternation of 

 developing egg on right, with undifferentiated primitive ova on left. 

 ( X about 650.) 



Plate 2. 



Fig. 21 a, b, c. — Nucleus of developing egg of spring generation, a and b are optical 

 sections of the nucleus at different levels, c part of the same nucleus in the 

 next section of the series. In b the chromosomes shown in outline are ends 

 of those seen in the same po.sitions in a. 



Figs. 22 to 33 represent the maturation of the summer egg. 

 Fig. 22. — Outline of section of egg showing stalk and polar mitosis. ( x about 650.) 

 Fig. 23. — Nucleus at edge preparing for maturation division. 

 Fig. 24 a, b. — Two successive sections of early stage of division. 



Fig. 25«, Z). — Polar views of first maturation division. a represents the inner, b the 

 outer chromosome group. Drawn from different levels in the .same section. 

 Fig. 27 represents nearly the same stage in side view. 



Fig. 26 a, b, c. — Later stage of maturation, a and b are drawn from different levels in 

 the same section, c from the next se'ction of the series, a represents the 

 innermost group, and some of the chromosomes in b are apparently 

 continuous with those in a. c represents the outermost group. 



Fig. 27. — Early stage of the first maturation division, side view. 



Fig. 28 a, b, c, d. — a and b are the two groups of polar chromosomes drawn from the 

 same section at different levels, c represents the spermatozoon becoming the 

 male pronucleus in the next section ; d, the insinking chromo.somes forming 

 the female ])ronucleus cut twice in the succeeding two sections. 



Fig. 20. — Early stage of second maturation division, unusual toiidition. 



Fig. 30 a, b. — Close of first and beginning of second maturation divisions ; two successive 

 sections of series, a shows outer group, b part of cuter and elongated iimer 

 group. 



fio. 31. End of second division of inner group. Chromosomes which form female 



pronucleus closely ])acked, below ; inner polar chromosomes and outer group 

 preparing to tlivide, above. Female pronucleus in next .section to polar 

 chromosomes, (x about 800.) 



PiQ. 32. Close of second maturation division. Clironuwomes of female ])ronucleus 



sinking in, outer group completing its division, .sp. represents the 

 spermatozoon becoming the male pronucleus, from the next section. ( x 800.) 



Fig. 33.— Female pronucleus {pr. v.) and three grou])s of polar chromosomes. 



Platk 3. 



Pio. 34. Meeting of male and female pronuclei. 



Fio. 35.— Conj\igation of pronucli^i and first scgnu-ntation spindlo. a and b mark the 

 cliromoHOJiie groups dci ivod from the two jjronuch^i. In the sei;tion they lie 

 at diflferent levels, so that they an; actually placed across the axis of the 

 spindle. 



Fio. 36 a, b. Two jjolar views of telophases of segmentation mitoses, showing about 



20 chromatin uijihsoh. Si<le view of same stage in fig. 38. 



