CHROMOSOME NUMBER AND PAIRS IN AMBYSTOMA 185 



have been many confirmatory observations and some that 

 oppose it. 



Montgomery ('01, p. 220) advanced evidence that for each 

 of the chromosomes of maternal origin there is a homologous 

 mate among the chromosomes of paternal origin, and that these 

 homologiies unite during synapsis. He also maintained that 

 these pairs^ can be recognized in the spermatogonia. This 

 view has been supported by many authors. Among these are 

 Sutton ('02), who compared numerous camera-lucida drawings 

 of spermatogonial complexes of Brachystola magna; Meek 

 ('12 a), who measured the lengths of spermatogonial chromo- 

 somes of a somewhat wide range of animals, and Hance ('17 b, 

 '18 a), who made linear measurements on the germinal and 

 somatic chromosomes of the primrose, Oenothera scintillans and 

 the pig. On the other hand, Meves ('11), on the basis of meas- 

 urements made upon the spermatogonial and somatic complexes 

 of Salamandra maculosa, fails to confirm the claim for the 

 former and denies it (p. 282) for the latter. Delia Valle ('12), 

 who measured the chromosomes of peritoneal cells of the same 

 form, also denies the existence of pairs. 



Some of the somatic cells studied in Ambystoma tigrinum are 

 quite favorable for a linear measurement of chromosomes, and 

 these complexes have been used to obtain further data upon 

 the query as to whether the chromosomes of the somatic cells 

 form a duplicate series (based upon length and form) as is shown 

 by their progenitors in the germinal line during the maturation 

 period. 



h. Mensuratio7i. Since the possibilities of error in measure- 

 ments are so great, it is necessary to consider the conditions 



2 The two mates constituting a pair are usually of equal length, so that homo- 

 logues may be recognized by such equality. In some cases, for example, in 

 the Diptera, Stevens ('08, 11), Metz ('14, '16 a and b), Holt ('17), Whiting ('17), 

 Hance ('17), the two members lie near each other or even closely approximated 

 in the spermatogonia and somatic cells, while in many other cases, for example, 

 in Orthoptera and Amphibia, the homologues may be widely separated in these 

 cells. In the present paper the term 'pairs' will refer to the two chromosomes 

 which are homologues as determined by length and form regardless of the 

 relative position in the cell. 



