384 



DESIGN IN NATURE 



PLATE LXXXVII 



PLATE LXXXVII (continued) 



(R, S, T.) Stages o£ metakiiiesis according to Rabl. 



R. The split chromosomes beginning to separate. 



S. The separation further advanced. 



T. The separated chromosomes passing along the fibres of the achromatic spindle. 



U. Gland-cell from a larva of nemocera. a, Cell membrane ; h, protoplasm ; c, nucleus with convoluted filament. 



V. Part of the nuclear filament seen at U greatly magnified (Carnoy). 



PLATE LXXXVIII 



Plate Ixxxviii. illustrates the formation and conjugation of the pronuclei in Ascaris megalocephala according to 

 E. V. Beneden. 



A. a, Female pronucleus ; h, male pronucleus, each containing two chromatin particles, the male (h) exhibiting skein formation ; 

 c, one of the polar globules ; the second polar globule has been extruded. 



B. The chromatin in the female (a) and male (J) pronuclei forming skeins ; r , polar globule. 



C. The skein formation of the female (a) and male (h) pronucleus more pronounced ; remains of spermatozoon adhering to b. 

 Two attraction-spheres (d) with central particles united by spindle of achromatic fibres now appear ; c, polar globule. 



D. The female (a) and male (h) pronuclei enlarged and skein formation completed ; c, polar globule. 



E. a, Female pronucleus with skein contracted and thickened ; d, attraction-spheres on one side of ovum connected with 

 periphery by cone of fibres forming polar circle (e, e') ; f, equatorial circle. 



F. Female (a) and male (ft) pronuclei now in contact ; spindle system arranged across their axes. The attraction-spheres {d, d), 

 placed between pronuclei. At G, H, I, and J, these spheres are omitted. 



G. Construction of skein and v-shaped formation of chromatin filaments in female (n) and male (b) pronuclei, which now indent 

 each other ; c, polar globule. 



H. V-shaped chromatin filaments more pronounced, and union of female (a) and male (5) pronuclei more intimate ; c, polar 

 globule. 



I. V-shaped chromatin filaments dividing by longitudinal cleavage a and h, male and female pronuclei ; r, polar globule. 



J. Highly magnified to show structure of v-shaped chromatin filaments {a, b) ; consist of fine granules of chromatin ; 

 c, polar globule. 



K. a, b, Four chromatin loops in middle of elongated ovum about to divide into two cells ; the loops forming a spindle-shaped 

 system of granule with fibrils radiating in the direction of the attraction-spheres (d, d'), which in turn radiate into the protoplasm 

 of the ovum ; c, polar globule. 



L. Shows chromatin filaments (a, b) of conjugated nuclei separating; also system of radiating fibres from attraction-spheres 

 {d, d') ; c, c , polar circle ; d, d', central circle ; e, equatorial circle (semi-diagrammatic). 



