68 SPERMATOGENESIS [CH. 



is sometimes convenient to use McCxuNc's term syndesis 

 to describe the union of threads or chromosomes in pairs; 

 the word synapsis is often used in this sense, but as it 

 is also used in the sense of synizesis (contraction of the 

 chromatin-threads into a compact mass), the word synapsis 

 tends to be misleading. The union of chromosomes in side- 

 by-side conjugation is called parasyndesis (parasynapsis), 

 and the end-to-end union (formerly supposed to be fre- 

 quent or universal) is telosyndesis (or telosynapsis). The 

 condition in which the chromatin is all arranged in looped 

 threads (formerly supposed to be one continuous coiled 

 thread, but now more frequently regarded as a number of 

 intertwined loops) is called the spireme, and the stage at 

 which the spireme by contraction of its loops gives rise to 

 the reduced number of short double chromosomes is dia- 

 kinesis. The appearance of half the somatic number of 

 double chromosomes in consequence of syndesis is often 

 spoken of as pseudo-reduction. 



The course of events in the meiotic or maturation phase 

 of the spermatogenesis of Lepidosiren is on the whole typical 

 of the corresponding stages in a large number of animals 

 and plants. At almost every step of the process, however, 

 there are points of detail, some of them of very great 

 theoretical importance, about which there are differences of 

 opinion. Frequently, no doubt, these disagreements among 

 observers depend on real differences in the behaviour of the 

 nuclei and chromosomes in different animals, for it can 

 hardly be supposed that the phenomena are quite identical 

 in such different groups as, for example, Worms, Insects 

 and Vertebrates. The surprising thing, in fact, is not the 

 existence of differences, but that on the whole they should 

 be so small, and that closely similar phenomena should be 

 found in all the higher animals and plants. In many points, 



