128 bulletin: museum of comparative zoology. 



both maturation divisions are held to be equational, since they are 

 undoubtedly a})parently longitudinal — are far from conclusive. As 

 has been so often urged by Montgomery and others, the true inter- 

 pretation of the maturation divisions must be sought in synapsis and 

 the early prophase, and until these stages are fully elucidated it is 

 impossible to arrive at conclusive results as to the significance of the 

 two divisions. From this standpoint a number of recent writers have 

 held that when there are two longitudinal divisions one is always re- 

 ductional. In the Orthoptera we may have both a transverse and an 

 apparently longitudinal division occurring in different chromosomes 

 during the same mitosis, although when their previous history is taken 

 into account it is evident that both divisions are fundamentally the 

 same. 



On the other hand, in the many instances where one transverse 

 and one longitudinal division have been described, we may reasonably 

 assume that the transverse division is probably reductional, even 

 though the early stages in the formation of the bivalent chromosomes 

 have not been fully worked out. However, even in such cases there is 

 apparently room for doubt, since according to Struckman (:05) a 

 transverse division may be equational. 



Korschelt und Heider (:02) in their extensive review of the subject 

 distinguish two types of maturation; the "eumitotic," where both 

 divisions are equational and the "pseudomitotic," where one is re- 

 ductional. The classical examples of the eumitotic type are the 

 vertebrates and Ascaris, where, as described by a number of earlier 

 investigators, two longitudinal divisions occur. But in the vertebrates 

 Montgomery (:03, :04), A. und K. E. Schreiner (:04, :05, :07), 

 Farmer and Moore (:05), and Janssens (:05) have found that one 

 division is reductional, and in Ascaris Tretjakoff (:04) and Marcus 

 (:06) have arrived at similar results, while Boveri (:04) has also 

 argued for the probable occurrence of a reductional division in this 

 form. 



De Sinety (:01) has described two longitutlinal divisions in various 

 Orthoptera and denies that either is a reduction division. His results 

 have been criticised at length by McClung (:02) so that it is unneces- 

 sary to consider them in detail here. However, I am unable to agree 

 in some cases with McClung's contentions. De Sinety's interpreta- 

 tion of the maturation divisions appears to be based almost entirely 

 on the larger chromosomes, where in some cases both divisions are 

 apparently longitudinal. I believe that this author correctly described 

 the division of the large ring- and loop-shaped chromosomes and that„ 



