220 First Maturation Spindle of Aliolobophora Foetida 



placed end to end. As they contract and are pressed together each splits 

 open along the line of the longitudinal furrow, the ends are thus pressed 

 out at right angles forming the two arms of the cross. As our prepar- 

 ations show the cross type of chromosome in all stages of its development, 

 no other explanation of its origin for this egg seems possible. The be- 

 ginning of the formation of a cross is seen in Photo. 124, Plate VIII, 

 in contact with the asymmetrical figure 8, and northeast of it a cross in a 

 further stage of development. Varying forms of the cross chromosomes 

 are seen in Photos. 117, 120, 123, Plate VIII, and 116, Plate VII. The 

 last photograph shows also the first stage of a cross formation in the 

 bivalent small chromosome at the lower periphery of the germinal vesicle, 

 and in Photo. 126, Plate IX, the method of forming a cross is almost 

 schematically shown in the fourth chromosome from the left periphery of 

 the photograph. 



In the jDreparations reproduced on Plate IX the membrane of the 

 germinal vesicle as well as the principal and accessory fiucIeoU have dis- 

 appeared. The eleven bivalent chromosomes in all cases are present and 

 in Photos 129 and 130 are symmetrically arranged in the equator of the 

 spindle ready to divide. These preparations appear to us to demonstrate 

 conclusively that the first division separates two univalent chromosomes, 

 but we do not yet know that these two univalent chromosomes are two of 

 the somatic chromosomes of the oogonia, so we cannot assert that the first 

 division is a reducing division in Weismann's sense. We can only say 

 that the prophases and metaphase of the first maturation spindle of 

 AUolohopliora support the observations of Korschelt, Montgomery and 

 others, who do claim that the first division is reducing. But in Allolo- 

 iophora several questions still remain unanswered. Does each bivalent 

 chromosome represent two somatic chromosomes which are exactly similar 

 in size and form, or does this exact similarity only indicate a foreshadow- 

 ing of the first division ? Do the two represent the paternal and maternal 

 inheritance as held by Montgomery, 'oi, Sutton, '02, and others, or 

 does the longitudinal furrow indicate this double line of inheritance ? We 

 must delay an attempt to answer these questions until we can determine 

 whether the pairs of chromosomes, represented by the bivalent chromo- 

 somes of the prophase, are present in the oogonia as Montgomery and Sut- 

 ton find them in certain insects, and whether tlie longitudinal furrow of 

 the prophase can be explained as a foreshadowing of the second division. 



The photographs of Plates VII and VIII demonstrate that the ring 

 chromosomes are formed by the uniting of the free ends of two univalent 

 chromosomes and the photographs of Plate IX show that such rings are 

 divided at the metaphase at the points of contact of these two chromo- 



