RESPIKATORY ORGANS JN ARANEA5. 
49 
As tlie youug spider, however, a.pproaches maturity, the 
attachment area aorain nndero-oes a considerable alteration in 
its form and. position, resulting mainly from two processes. 
These consist in (1) the formation of a transverse in-folding 
of the hypodermis (the interpulmonary fold) between the 
two spiracles, which thus become connected by a deep 
ventral groove ; and (2) the drawing-out in the fonn of a 
blind tube (entapophysis) of the dorsal edge of this fold at 
the two spots to which the pair of mesodermal entochondrites 
are attached. 
The interpulmonary (epigastric) fold in the adult of Attus. — 
Fig. 20 represents a posterior view of the abdominal chitinous 
skeleton of an adult of a species of Attus, after the removal 
of everything posterior to the transverse plane which passes 
through the spiracles. It will serve to illustrate the form of 
the interpulmonary fold in the adult. 
In Attus floricola the interpulmonary fold in the male 
differs greatly from that of the female. 
Figs. 23-2dB are three sagittal sections through this fold 
in the adult male in the regions indicated in fig. 20. The 
much crumpled, anterior and posterior surfaces of the groove 
contained in the fold are normally closely applied to each 
other, so as to leave very little space between them. Along 
the dorsal edge, however, this is not the case, for here the 
groove suddenly widens to a nearly cylindrical canal {can.), 
which opens on each side into the pulmonary ante-chambers 
at their medio-ventral corners, thus forming a permanently 
open communication between the two lungs canal of com- 
munication” observed b}' Berteaux (’89) in Agelena and 
Kpeira]. The chitinous wall of the canal is thick and 
covered with branched anastomosing spines, quite similar 
to and directly continuous with those of the ante-chambers. 
The two entapophyses (ec. t. 8) have each the form of a 
short, strongly compressed pouch, whose blind end is 
directed upwards, backwards and laterad. The cavity in the 
ventral part of each branches off from the interpulmonai’y 
canal, and is provided, like the latter, with anastomosing 
VOL. o4, PART 1. — NEW SERIES. 4 
