BEHAVIOR OF NUCLEUS AXD CHROMOSOMES. l6l 



spends to the hyaline portion of the vesicle considered above, and 

 as such is similar to that in Lasiopogon. But his conception of a 

 -heath as characteristic of animal chromosomes and possibly also 

 of plant chromosomes, seems to us to be open to serious question, 

 at least in the form stated. It has been considered at length in a 

 recent paper by de Litardiere ('21), who interprets the "sheath" 

 as an artifact probably a fixation product. The latter author 

 maintains that the same sort of zone is to be seen around the 

 mitochondria, cytoplasmic inclusions, etc., and hence has no 

 special connection with chromosomes. We may omit further 

 consideration of these structures, therefore, until the evidence 

 becomes clearer. 



Possibly de Litardiere's criticism may apply to the cases we 

 have cited here of "indications" of a hyaline zone around chro- 

 mosomes in the Diptera, including spennatogonial chromosomes 

 of Lasiopogon; and it may apply to the zone seen in Mr( "lung's 

 figures referred to above. Further evidence is required to settle 

 this point. But we may note that in these cases the zone seems 

 to be found only around the chromosomes, not around other 

 structures in the cell. 



It may be added that in the case of the spcrmatocytes of Lasio- 

 pogon described here the structures are clearly not artifacts, and 

 are confined to the chromosomes (including the nucleolus which, 

 from analogy with other Diptera, is assumed to be chromosomal 

 in nature). Numerous large mitochondria! rods are present, but 

 are not surrounded by sheaths comparable to those enveloping 

 the chromosomes. 



If we omit the questionable cases, such as those just mentioned 

 as possibly due to artifacts, it is clear that few forms exhibit 

 structures comparable to those in Lasiopogon, although the possi- 

 bility still remains that the structures may be present in other- 

 ii when not visible. 



In the foregoing discussion little emphasis ha- l>r< n laid on the 

 fact that some of the cases considered involve bivalent chromo- 

 somes (maturation stages) and others univaknt chromo-omc-. 

 It is not yet clear that any distinction should be made, so fai 

 the present subject is concerned. But it may l-e noted in clo-iu;c 

 that any view which considers the chromosome .1- rncli.-cd in a 

 -heath or envelope must take account of the approximation of 



