64 SPERMATOGENESIS [CH. 



converging towards one pole of the nucleus, and branching 

 out into a network of fine threads which still occupies its 

 distal hemisphere. Gradually the pairing of the threads 

 proceeds further and further, while at the same time they 

 become shorter and thicker, with the result that in a short 

 time the network in the distal hemisphere is entirely un- 

 ravelled, and the nucleus contains only a number of double 

 threads arranged in long loops or horse-shoes, of which the 

 free ends converge towards the pole where the fusion first 

 began (E, F). The number of these loops is half that of the 

 somatic chromosomes. This stage is often spoken of as the 

 " bouquet " stage, and is followed by a rapid shortening and 

 thickening of all the threads, which become more or less 

 closely tangled together towards the pole of the nucleus in 

 a tight mass from which loops project into the nearly empty 

 distal half (F, G). This contraction and crowding together 

 was originally called synapsis, but as the word has been 

 used in two different senses McCLUNc's term synizesis is 

 preferable 1 . The contraction and crowding make detailed 

 observation difficult, but from the examination of exception- 

 ally clear nuclei, and from comparison with other animals, 

 AGAR is convinced that the threads which paired in the 

 bouquet stage have now separated again except at their 

 ends, with the result that there are now half the somatic 

 number of elongated, twisted rings, composed of threads 

 in pairs attached to each other at their ends but otherwise 

 single (G). These threads are now much thicker than 

 they were before the parallel conjugation, owing to their 



1 As was mentioned earlier (p. 56 note) HARDY has imitated the synizesis 

 stage of spermatogenesis in resting somatic nuclei of plants by passing through 

 them an electric current. The greater part of the chromatin became collected 

 at the side of the nucleus toward the positive pole, with loops extending into 

 the distal half, just as in synizesis the chromatin is contracted towards the 

 pole nearest the centrosome. 



