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 
homologues unite during synapsis. He also maintained that 
these pairs 3 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 (’ll), 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. Della 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. 
b. Mensuration. Since the possibilities of error in measure¬ 
ments are so great, it is necessary to consider the conditions 
8 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, ’ll), Metz (T4, T6 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. 
