A Preliminary Account of the Spermatogenesis of Sphenodon. 349 



Stenobothrus, Lepidosiren) may now be regarded as established, 

 and creates an overwhelming presumption in favour of the 

 applicability of the same scheme to a vast range of animal forms 

 showing similar features in general, even though points of detail 

 remain obscure. Nowadays, therefore, the field of discussion with 

 reference to the mode of reduction narrows down to the claim of 

 those who advocate telosynapsis that in certain cases a leptotene 

 stage is wanting. This purely negative proposition loses much 

 of the cogency it might otherwise possess for two reasons : first, 

 that the stage in question is very refractory to fixation ; secondly, 

 in many cases where earlier work failed to reveal such a phenomenon 

 subsequent study has shown that it does actually exist, as in the 

 case of certain Orthoptera and Platyhelminthes. Since it is the 

 concern of a scientific hypothesis to interpret phenomena in terms 

 of experience, it rests with those who advocate terminal conjuga- 

 tion to provide an alternative method of deriving the reduced 

 segments of the universally characteristic diplotene stage' from the 

 chromosomes of the spermatogonial telophase. The earliest theorists 

 made use of the conception of a continuous spireme in the normal 

 interphase, as introduced by Flemming's school, to envisage the 

 process ; but the more precise knowledge of the relation of meta- 

 phase chromosomes to the constitution of the resting nucleus 

 gained of recent years through the work of Bolles Lee, Bonnevie, 

 Digby, Gates and others dismisses from further attention the 

 adherence in pairs during the meiotic phase of chromosomes 

 formed by the segmentation of a continuous spireme. There is no 

 sound justification for entertaining the reality of synapsis, unless 

 definite evidence can be advanced in favour of the underlying 

 assumption of the persistence of chromosomes in the germ-cell 

 cycle as integral units ; and direct information on this point 

 involves a recognition of the fundamental discontinuity of the 

 elements in the so-called spireme (pro- and telophase) stages. 

 The objections of Meves, Pick and Duesberg, who, reserving a 

 sceptical attitude to the persistent individuality of chromosomes, 

 maintain that the character of the reducing division in certain 

 forms is incompatible with a belief in parallel conjugation, is 

 therefore more intelligible than the standpoint recently revived by 

 Nakahara. For while it may still provide scope for profitable 

 enquiry to elucidate the compatibility of the genesis and subsequent 

 fate of the heterotype chromosomes with the parasynaptic view as 

 a critique of the actual validity of synapsis, the hypothesis of 

 telosynapsis, it appears to me, will only necessitate reconsideration 

 (as applied to animals) when it is possible to rehabilitate it in 

 terms that are consonant with accredited facts respecting the 

 kinetic processes both in tlie premeiotic and meiotic phase. 



The frequently very complicated metamorphosis which is 

 involved in the transformation of the diplotene segments into the 



