560 
W. F. PURCELL. 
entire body witli tracheoe, the anterior pair did not further 
increase in size. 
In the second place, in the progenitor (or progenitors) of 
the remaining tracheate spiders, the posterior lung-books 
became reduced in size and eifectiveness by the disappear- 
ance of their saccules, accompanied by an increase* in the 
number of the leaves of the anterior lung-books. Further, 
the posterior spiracles became approximated and united to a 
single spiracle, and moved towards the hinder end of the 
body, thereby causing the entapophyses of the tracheal 
segment to elongate. In this condition the Filistatidae, 
8 icariid U3, and Palpimanida) have remained, with slight 
modifications, such as the division of the tracheal ante- 
chambers into branches in some forms. In the great majority 
of the families, however, the elongated entapophyses became 
transformed into a pair of medial tracheal trunks, thus pro- 
ducing a tracheal system consisting of four simple nnbranched 
trunks, which is still found in some genera at least, in nearly 
all the families. A new factor having been introduced, viz. 
the presence of the respiratory entapophyses lying in the 
large ventral sinus containing venous blood requiring aeration, 
we accordingly find the second respiratory segment again 
taking a prominent part in the respiration in many forms, 
owinar to the increase in size and the braiichinof of the medial 
trunks, accompanied ultimately by a corresponding reduction 
in the size of the anterior lung-books, e. g. in the Attidm. 
This method of origin of the tracheaa is independent of that 
of the Dysderida; and its allies, and the tracheal tubules, 
when present, would here not be derived from saccules, but 
be new formations. 
List of Literatoke. 
’72. Bertkau, P. — “ Ueher die Respirationsorgane der Araneen,” ‘ Arch, 
f. Naturg.,’ xxxvdii, Bd. i, pp. 203-2.33, 1 PL, 1872. 
“Ueher den Generationsapparat der Araneulen," ‘Arch. f. 
Naturg.,’ xli, Bd. i, pp. 23.j-2(52, PI. vii, 187-5. 
’ 75 . 
