520 
W. F. PURCELL. 
provided that it be not interpreted to mean the development 
of the tracheae out of lung-books separately in each family 
but merely the development of more complicated tracheal 
systems from simpler ones or vice versa. 
Another important point which Lamy has emphasised 
(p. 264) is that the number of the lung-leaves is in inverse 
ratio to the size of the tracheal apparatus. Thus^ forms with 
highly-developed tracheee have a small number of lung- 
leaves, as Dictyna, with 4 — 5 leaves (Bertkau), Segestria, 
with 10 — 12 (Bertkau), etc., while forms with a feebl 3 '-deve- 
loped tracheal system have a comparatively large number of 
lung-leaves, as Bpeira and Agelena, with 60 — 70 leaves 
(Bertkau). 
Since the i-elative size of the tracheal apparatus in general 
increases proportionately with its degree of complication it 
further follows from the above paragraphs that the number 
of the lung-leaves in forms having both tracheae and lung- 
books can have no greater ph 3 dogenetic value than that pos- 
sessed by the degree of complication (in respect to branching 
and internal armature) of the tracheal apparatus and this 
Lamy has shown to be of subordinate phylogenetic value, 
without even the importance of a family character. We 
cannot, in fact, use either of these characters in comparing 
widely remote families ph 3 dogenetically, as, for instance, the 
Dysderidae and Argiopidm (Epeiridse). Thus, assuming 
that the tracheae were derived from lung-books, it would be 
incorrect to argue that an Argiopid, with its numerous luiig- 
leaves and simple tracheae is, on that account, a more primitive 
form than a Dysderid, with its few lung-leaves and large 
complicated tracheae ; or, conversely, if we admit that the 
Dysderidae are more primitive than the A rgiopidae, we 
could not argue that because of the different relative develop- 
tnent of these two organs in the two families, the lung-books 
must have been derived from trachefe. 
It does not follow, however, from any of Lamy’s arguments, 
that the two characters just discussed ai’e of no ph 3 dogenetic 
importance at all, e. g. amongst allied genera in one and the 
