THE PHASE OF THE NUCLEUS KNOWN AS SYNAPSIS. 593 



ance is tliat of a balled up mass of lumps or granules, and sometimes that of chromatin 

 thread." 



Among the Fungi, synapsis has been found by Miss Fraser (1908). She describes 

 it in her account of Humana : " The stainable material of the nucleus forms a fine 

 threadwork and becomes aggregated towards one side of the nuclear membrane, forming 

 the first contraction figure, as has been described for the spore-mother-cells of the 

 higher plants." 



For the Ferns we have an account of synapsis in Nephrodium by Yamanouchi (1908). 

 His account is as follows : " As described before, the nucleus in the pre-synaptic stage 

 consists of a complex, anastomosing, chromatin reticulum. This ragged reticulum 

 shows a tendency to become transformed into a thread structure, but the process does 

 not occur simultaneously in the different regions. When the transformation has taken 

 place, the two parts of the thread are observed running side by side from the first. 

 Such a condition, etc., is evidently what was called 'leptonema' by Winiwarter. 

 Further transformation of the thread structure from the ragged reticulum results 

 in a nucleus with a continuous chromatin thread in a spireme whose double nature is 

 only visible at certain parts on account of the close association. The thread becomes 

 tangled and contracted in one side of the nuclear cavity until finally there results the 

 climax of the synaptic stage. . . . There are observed in Nephrodium a number of 

 parts of the spireme running through the contracted mass from the nuclear membrane 

 where the mass lies in contact." 



Even in the more recent literature the contracted condition of the chromatin is fully 

 described and its relation to the reduction process is emphasised. In his work on the 

 organisation of the nuclei in pollen-mother-cells, Overton (1909) states that the first 

 indication of synaptic contraction in Thalictrum purpurescens consists in a concentration 

 of the paired spireme threads either in the centre or at one side of the nuclear cavity, 

 so that the nucleus appears much more open and clear than at earlier stages. 

 " During the earlier stages of this contraction the threads which constitute the frame- 

 work are present, but then later disappear as the whole mass rounds up. In my former 

 paper I have described the phenomenon of synapsis, which I held to be a normal process, 

 in which a union in pairs of homologous elements is brought about with a consequent 

 pseudo-reduction. Although synapsis was described as a phase, during which a mutual 

 interchange or interaction of parental elements might occur, I also expressed the opinion 

 that the homologous chromosomes retain their identity during the process." 



In his work on (Enothera, Davis (1909) defines synapsis as a "general slow con- 

 traction of the reticulum away from the nuclear membrane, a contraction that carries 

 most of the strands towards the centre of the nucleus. During the process of contraction 

 numerous threads are differentiated from the reticulum, which become coiled in a very 

 intricate manner." Davis further describes how " the synaptic contraction draws the 

 coils of threads into a dense knot close to the large nucleolus, which generally lies at one 

 side of the nucleus. Loops of the threads extend into the nuclear cavity from the 



