Katharine Foot and E. C. S.trobell 221 



somes. In most cases this point of contact is expressed by a clear space 

 or by a knob-like thickening. The clear space is shown in the three rings 

 of Photo. 117, Plate VIII, and in one or more of the chromosomes in 

 Photos. 116 to 130, Plates VII, VIII and IX. The knob-like thickening 

 at the point of contact of two univalent cliromosomes is shown in one of 

 the chromosomes of Photos. 116 and 130. 



That the spindles must have some tenacity of form in the living egg 

 is demonstrated by the characteristic spindle formation with the two polar 

 spheres often remaining undisturbed by the process of pricking the 

 membrane of the egg and allowing the cytoplasm to flow out upon the 

 slide. An indication of the spindle form is shown in Photos. 125, 128, 

 129 and 130, Plate IX. The fact that the egg is dried so rapidly that 

 the form of the spindle is not distorted argues that some confidence may 

 be placed in the form of the chromosomes as well. 



In the equator of the spindle of Photo. 125, Plate IX, a ring chromo- 

 some is seen showing a distinct longitudinal split and the clear transverse 

 sj)ace which indicates one point of contact of the two univalent chromo- 

 somes which form the ring. This space is in the equator and unquestion- 

 ably indicates one of the points of separation of this chromosome. The 

 chromosome on the extreme left shows a like clear space, the other half 

 of the ring, having already separated and contracted, resulting in one of 

 the forms typical of the metaphase (the lower arm of this chromosome 

 is in contact with the upper arm of a like chromosome). This form of 

 division is seen in two of the chromosomes of Photo. 128, in at least five 

 of the chromosomes of Photo. 129 and five of Photo. 130, Plate IX. 

 Rings with a longitudinal furrow and characteristic indications at the 

 points of contact of the univalent chromosomes of which they are formed 

 are shown in Photo.- 126, Plate IX, and three similar rings dividing 

 transversely are shown in Photo. 127, the one near the center of the 

 photograph being especially instructive. These examples, with the ring of 

 Photo. 129 and the two rings of Photo. 130, Plate IX, appear to dispel 

 all doubt as to the manner in which the bivalent chromosome of Allo- 

 lohophora is divided in the first maturation division. In each of these 

 six photographs there are examples also of the simple transverse separ- 

 ation of the two rods attached end to end which represent the simplest 

 form of these bivalent chromosomes. Many of them still show the 

 longitudinal furrow which has persisted from the spireme stage and 

 leave no doubt that this division is not along the lines of this longitudinal 

 split. 



^lany of the chromosomes demonstrated in the spindles of our Plate 

 IX closely resemble those figured by Nelcrassoff, '03, in the first matur- 

 16 



