216 CHARLES W. METZ 



parental series (haploid groups), the individual members of 

 which are respectively homologous and very similar to one 

 another; and this involves the view that the chromosomes are 

 present in bi-parental pairs (Montgomery, Sutton, Boveri). 

 In addition it is supposed, in accordance with the conception 

 of W. Roux that every chromosome contains a definite comple- 

 ment of serially arranged genetic factors, each responsible for 

 one or more inherited characters — the complement of factors being 

 the same or similar in homologous chromosomes (members of a 

 pair) but different in non-homologous chromosomes. In order 

 to explain the perpetuation of this duplex germinal constitution 

 a process (reduction division) is assumed to occur during matura- 

 tion whereby the members of each pair are separated from one 

 another and segregated in different germ-cells. 



From the cytological point of view the principal questions 

 involved in this theory are as follows: 1) Can definite pairs of 

 chromosomes really be distinguished? 2) If so, are the two 

 members of a pair derived respectively from the male and fe- 

 male parents? 3) Are the two members of a pair actually simi- 

 lar to one another and qualitatively different from the others 

 in respect to their physico-chemical constitution? 4) Do the 

 two members of a pair actually separate from one another and 

 go into different germ-cells during maturation? 



Three of these questions, together with one other of a more 

 strictly cytological nature — the question of synapsis — fonn 

 the central points about which most of the facts considered in 

 the present study may be grouped. The nature of the material 

 prevents the detailed consideration of each question in the order 

 given, but so far as possible the evidence is presented in accord- 

 ance with this scheme. The evidence bears especially upon the 

 first question, to which a definite affirmative answer is given. 

 With respect to the second question judgment should, perhaps, 

 be suspended until the genetic continuity of the chromosomes 

 is established, but if this continuity be assumed, this question 

 is likewise answered in the affirmative. Regarding the third 

 question only indirect evidence is furnished, but this evidence 

 lends support to an affirmative answer here also. The fourth 



