70 
AV. ¥. rUL’CE],L. 
truuks only to be equivalent to the lateral trunks in other 
spiders. 
The tracheae in Ai’gyroneta aquatica. — The highly-developed 
tracheae ^ of this water spider are very peculiar. The two 
main branches, as Bertkau (’78) showed, have a common 
sjeiracle, which opens far forwards (text-fig. 4), close to the 
pulmonary spiracles. The remarkable point about these 
trachete is the circumstance that they lie entirely on the 
medial side of the longitudinal ventral muscles. The seg- 
ment of this muscle belonging to the tracheal somite is very 
short, corresponding to the anterior position of the spiracle, 
and it is stretched between two large entochondrites, the pos- 
terior of which is attached to the upper surface of a short 
basal process on the lateral side of the tracheal trunks. This 
process, which is figured by Lamy (:02, p. 212, fig. 56), is 
provided in its cavity with spines, like the main trunks, and 
gives off at its apex a number of fine tracheal tubules (the 
lateral bunch of trachem described and figured by Menge 
[’51, dd, PI. i, fig. 7] and Lamy). 
The process is flattened dorso-ventrally and corresponds to 
the tendinal trunk of other Uipneumonous spiders. The two 
large main trunks appear to be outgrowths from the medial 
side of each very short tendinal trunk. They are joined at 
their bases by an intertracheal fold provided with the usual 
spinous canal of communication. On the posterior side of 
each main trunk, near its base, is a transverse out-folding of 
the tracheal wall forming a deep spinous groove ou the inside 
of the trachea, connecting the canal of communication with 
the lateral or tendinal branch. This transverse folding, Avhich 
was described by Bamy (:02) as an abdominal trunk resembling 
that in Segestria, also gives off numerous tubules, which, 
together with another group just below, springing directly 
from the main trunk, form the posterior bunch of tracheaj 
figured by Menge (’51, ee., PI. i, fig. 7). 
In Argyroneta, therefore, the entire tracheal 
' Literature : Grube (’42), Menge (’51), Bertkau'.('78, p. 384). MacLeod 
('80. "84), Lamy (.02). 
