EESPIBATORY ORGANS IN ARANE/E. 
11 
All these parts, being hollow, contain air in direct com- 
munication with the external atmosphere. The partition walls 
between the air-spaces of adjacent saccules, I shall term the 
‘‘septa.”i The dorsal side of each septum is studded Avith 
numerous, simple, blunted spines, which keep the lumens of 
the saccules open, while the walls of the ante-chamber 
(including its fenestrated anterior wall and the apical pouch 
of the horn), are covered with pecnliar hooped spines 
(spines with anastomising apical branches). The pedicel is 
for the most part unspined. 
The two spiracles are generally united by a transverse 
fold, the epigastric or interpulmonary fold {interp. 
fill.), which also connects the two pedicels and the extreme 
medial corners of the two ante-chambers (see text-fig. 1). 
The lumens of the latter at the same time communicate by 
the interpulmonary canal of communication (can.), or 
passage Avitli hooped spines in the upper edge of the fold. 
Further remarks on the lung-books of the adnlt are given 
on p. 41, and an historical account of the literatnre will be 
found at the end of the paper. 
Tracheae. — The usual form of tracheae in a Uipneuinonous 
spider has the folloAving parts (figs. 21, 25 and 31) : 
(1) A median, transverse, ventral spiracle (sj).), placed 
on the hind mai-gin of the third abdominal segment usually 
just before the spinners (text-fig. 1). 
tlie procAirvecl honi is wrongly represented as having no saccules opening 
into it. 
‘ In order to avoid ambiguity I have substituted the terms "sac- 
cules” and "septa” in place of the old terms "leaves” and 
"lamellai.” The older writers almost invariably meant to indicate the 
saccules when they used the term "leaves” (feuillets, Blatter), 
but since about 1881 the term has generally been employed for the septa, 
like the term " lamellae.” Neither term, however, has at present tniy 
definitely recognised use. Thus "lamelles” signifies the septa with 
MacLeod ("84), but only one of the layers of a septum Avith Berteaux 
('89), Avhose term for a Avhole septum is “lame,” Avhile "feuillet” 
signifies a septum Avith SchiuikeAvitsch ('84) and Plateau ('86), Imt a 
saccule Avith Scl)neider ('92). 
