CHROMOSOMES IN COREID HEMIPTERA. 95 



ducing" spermatozoon, i. e., one bearing the idiochromosome 

 (directly proved in Archimerus, but only in part in Anasa and 

 Protcnnr). The idiochromosome bivalent is not distinguishable 

 l>y its behavior from other chromosomes, and divides in both 

 mitoses, giving an equal portion to each ootid. It never assumes 

 a run -h-ohi like form either in the oogonial or oocyte divisions. 



B. Some Details of Polar Body Formation. 

 The pi. ire of polar body formation has been found to vary in 

 different ^n mp- of insects. It may be on the dorsal surface, 

 either ,ippro\im.itely midway between the poles as in Blatta 

 i Blo< hmann, XYheeler) and Pyrrhocoris (Henking), or a short 

 di-iance behind the anterior end as in Musca (Blochmann, Hen- 

 kin. . In ( hrysomelidae (Hegner) it is ventral, while in Pieris 



II. nl in. ii is close to the anterior (micropylar) end. In 7/v- 

 drnplnlns > Heider) and Aphis (Stevens) it is lateral. In A r chi- 

 me r us the polar bodies are given off on one of the flat surfaces of 

 the approximately midway between ^the poles. In this 



spei iea the two surfaces cannot be distinguished after the chorion 

 ha- been renio\ed. but in Protenor the dorsal surface is markedly 

 convex \\hile the ventral is flat or slightly concave, and it was 

 hen- drier-mined by proper orientation that the place of polar body 

 forrn.il ion i- on the dorsal surface. The first polar spindle lies 

 in a -in. ill thickening of cytoplasm with its axis at right angles 

 to the egg Miitace (Fig. i,/ and g; Fig. 4, a and b; PI. I., a). 

 The .ui.iph.iM- of the first polar division occurs just after laying 

 (in Artliinti-rus a single exception was found; see footnote 9, 

 page 'H \'o centrosomes or asters could be demonstrated 

 b\ the method of fixation used just as Henking ('92) found in 

 Pvrrhth-oris though he used a different method. In late anaphase 

 .i cell-plate i- formed by swelling of the spindle fibers and the 

 MII t.ne of the egg dips down and around the outer group of 

 chronio-onies, until finally a little mass of cytoplasm containing 

 the 1. itter comes to lie free in a depression of the egg surface 

 (J-'ij.. i. < and g; Fig. 4, b\ PI. I., a). In both the first and the 

 second polar divisions (Fig. 4, b, and PI. I., b) the constriction 

 probably does not involve the cell-plate but passes between it 

 and the outer group of chromosomes as Henking observed in 



Pyrrhocoris. 



