552 
W. F. PUItCELL. 
in the anterior tracheee, and. by the addition of the short 
posterior branch in place of the medial basal group of tubules. 
In such case the bunch of tubules at the anterior end of the 
cephalothoracic trunks {ceplb.tr.) would represent metamor- 
phosed pulmonary saccules, but those of the posterior abdo- 
minal branch {ahd.tr.) would be, of course, new formations. 
In a previous paper (:09) 1 had already indicated the 
possibility of the anterior bunch of tubules being derived 
from saccules, but after studying the tracheae of Capouia 
more thoroughly, I am now much more strongly inclined to 
believe that such has actuall}" been their origin. A study of 
the embryology would, however, be necessary to settle this 
interesting point. 
If, as I have assumed, the posterior pair of trachete in 
Capouia aud those in the Dy sderidie had a common origin, 
it follows that the auteilor pair of trachea) in the former must 
have developed later and independently of the posterior pair, 
and that, therefore, trachea) must have originated from 
lung-books at least twice in the Aranem. The same 
conclusion would follow even if we assumed that both pairs 
of trachea) iu Capouia originated at the same time and not 
as separate metamorphoses, for in that case both pairs of 
trachem must have originated independently of those of other 
tracheate spiders, since these latter still possess the anterior 
pair of lung-books. 
The mor])hology of the respiratory segments bears out the 
view that the three families discussed above are intermediate 
in position between the mygalomorphous spiders and the rest 
of the arachnomorphous forms. This view was demonstrated 
by Bertkau (’78) a good while ago for the Dysderidm and 
the Oonopidae, and this author even went so far as to 
include these families Avith the mygalomorphous forms in a 
common group, the Tetrasticta (i. e. Avith four stigmata). 
No doubt these tAvo families are the most primitive of the 
three, but the Caponiidae may be considered as an allied 
but in several respects a very aberrant t} pe, standing apart 
from the other tAvo families. 
