1974 ] 
Cooper — Boreus 
99 
tory duct,” is very likely the large retractor muscle in my figure 2B 
which occupies that position in B. notoperates. Brief comment on 
the aedeagus of Boreus will be found in Fitch (1847), Kolenati 
(1847), Cockle (1908, 1914), and Byers (1954), as well as in 
Withycombe (1926) and Crampton (1918, 1920, 1923, 1931) who 
have figured it in an everted state. To judge from these figures and 
my own, species of Boreus may differ in the apical morphology of 
the aedeagus. 
Cytology 
Boreus notoperates has a diploid number of 20 in the female and 
19 in the XO male. At spermatogenesis, the autosomes are conjoined 
by chiasmata (nearly always but one per bivalent) that are interstitial 
or proterminal at diakinesis, but for the most part terminalized by 
metaphase-I. There is only a moderate premetaphase stretch. 
The acrokinetic X is the largest chromosome of the set (from 
7-9 jx long), being respectively two to five times the lengths of the 
largest and smallest autosomes. The X possesses a nucleolus organ- 
izer proximally in the long arm. Spermatogenesis is orthodox, the X 
segregating precociously and reductionally at anaphase-I. At ana- 
phase-II, as at anaphase in both spermato-and oogonial mitoses, the 
separating chromatids of X stretch and span the entire length of the 
elongating spindle before their distal tips disjoin. 
The chromosome number of B. notoperates is the lowest so far 
known for Boreus (B. bru?nalis J , ncf — 11+ XiX 2 ,Y; B. hy emails, 
ncf ' — ' 14 + X, 0 ; B. nivoriundus ncf — 15 + X, 0 ; Cooper 1951 
and unpubl.) ; except possibly for a cytological form of Nannochorista 
dipteroides Till, (n = 9 ?, Bush 1967), it is indeed the lowest num- 
ber so far claimed for Mecoptera. A second strain of N. dipteroides 
(n — ca 14), Chorista australis Klug. (ncf = 14 + X, 0 ) (both 
in Bush 1967), and three species of Bittacus (ncf — 13 + X, 0 ; 
ncf — 14 + X, 0 ; ncf = 15 + X, 0 ) (Matthey 1950; Atchley 
and Jackson 1970), all lie within the range of Boreus. My prepara- 
rations of a single male of Merope tuber Newm. display chiefly very 
drawn-out early diakinetic chromosomes, and are sufficient only to 
establish that it is XO, chiasmate, and has a haploid number that is 
less than ncf = 12 + X ,0 — possibly ncf — 10 + X, 0 . Though, 
at this time no more definite statement can be made for our most 
primitive mecopteran, it is nevertheless clear evidence that the chro- 
mosome number of Merope is not a relatively high one. On the other 
