88 
Psyche 
[September 
discussed chromosome evolution in the genus Drosophila in detail. 
Several investigations have been made concerning the cytology of 
the Tephritidae. Metz (1916), after investigating the chromosomes 
of Euresta melanogaster Loew [probably Dyseuaresta mexicana 
(Wied.)], concluded that flies of the family Tephritidae were not 
suitable for detailed chromosome studies. He did state, however, 
that this species appeared to have a haploid number of six, though 
he presented no figures. Keuneke (1924), on the other hand, 
obtained clear metaphase complements from Tephritis arnicae L., 
which had an interesting XO instead of the normal XY sex deter- 
mining mechanism found in most Diptera. This configuration resulted 
in a diploid number of 1 1 in the male and 12 in the female. A reduced 
number of chromosomes has also been reported for A. ludens by 
Emmart (1935). A haploid number of 5 was found in spermato- 
genesis, though the findings of the present study do not support these 
observations for this species. 
In more recent studies, Frizzi and Springhetti (1953) described 
the karyotype of the olive fruit fly, Dacus oleae Gmel., as having a 
haploid number of 6. This same modal number of 6, which seems 
to be common in most higher Diptera (White, 1954), has also been 
reported for six out of seven species of Queensland Dacinae by Davis 
( 1 955 ) . One species had a haploid number of 7. Davis apparently 
encountered some technical difficulty, as he was unable to observe 
any details in the morphology of the chromosomes. Mendes (1958), 
however, was able to find distinct morphological differences in the 
chromosomes of two species of Brazilian tephritids, Anastrepha 
fraterculus (Wied.) and Ceratitis capitata (Wied.), both of which 
had the characteristic haploid number of 6. His description of the 
karyotype of A. fraterculus is of particular interest in that he found 
morphologically differentiated sex chromosomes. These distinguish- 
able heterochromosomes were not found in the Mexican population 
of this species by the author. The importance of these differences 
will be discussed later. 
Methods 
The chromosomes of the following nine species of tephritids were 
analyzed during the course of this investigation: Anastrepha ludens 
(Loew) ; A. zuelaniae Stone; A. fraterculus (Wied.) ; A. mombin- 
praeoptans Sein; A. distincta Greene; A. spatulata Stone; A. striata 
Schiner; A. serpentina (Wied.) ; and A . aphelocentema Stone. 
Larvae were reared from field collected fruit which was held in 
