IV] AND STRUCTURE OF THE CELL 315 



it is at least plain that by some physical cause, some mutual 

 attraotion or common repulsion of the particles, we must seek to 

 account for the symmetry of the so-called "tetrads," and other 

 more or less familiar configurations. The remarkable annular 

 chromosomes, shewn in Fig. 95, can be closely imitated by loops 

 of thread upon a soapy film, when the film within the annulus is 

 broken or its tension reduced ; the balance of forces is here a simple 

 one, between the uniform capillary tension which tends to widen out 

 the ring and the uniform cohesion of its particles which keeps it 

 together. 



We may find other cases, at once simpler and more varied, where 

 the chromosomes are bodies of rounded form and more or less 



Fig. 95. Annular chromosomes, formed in the spermatogenesis of the 

 mole-cric'iict. From Wilson, after Vom Rath. 



uniform size. These also find their way to. an equatorial plate; 

 we gather (and Lamb assures us) that they are repelled from the 

 centrosomes. They may go near the equatorial periphery, but they 

 are not driven there; and we infer that some bond of mutual 

 attraction holds them together. If they be free to move in a fluid 

 medium, subject both to some common repulsion and some mutual 

 attraction, then their circumstances are much like those of Mayer's 

 well-known experiment of the floating magnets. A number of 

 magnetised needles stuck in corks, all with like poles upwards, are 

 set afloat in a basin; they repel one another, and scatter away to 

 the sides. But bring a strong magnet (of unlike pole) overhead, 

 and the little magnets gather in under its common attraction, while 

 still keeping asunder through their own mutual repulsion. The 

 symmetry of forces leads to a symmetrical configuration, which is 



