38 
W. F. PURCELL. 
Sagittal sections, like Simmons’ figs. 5 and 6, therefore, cut 
the appendage more or less transversely to its main axis, 
which in the two figures would be, not in the plane of the 
paper, but almost perpendicular to it. 
In fact I cannot believe tliat the appearance of the a])peu- 
dage in Agel ena n gev ia at this stage differs so essentially 
from the corresponding stage in Attus floricola, such as 
that represented by my fig. 1(5. A sagittal section in the 
case of the appendage represented in this figiu'e would, of 
course, be more or less perpendicular to the plane of the 
paper and cut the appendage parallel to the line ep.-ep. If 
the section were slightly more inclined towards the lower part 
of the paper (say along a.-h., fig. IGn) we should get a section 
like fig. 15, but if it were inclined more towards the upper 
pai-t of the paper (say along c.—d., fig. 16 b), we should get 
sections exactly resembling Simmons’ figs. 5 and 6, according 
as two or five of the furrows were cut. This 1 believe to be 
the true explanation of the appearance of Simmons’ figures. 
It is extremely difficult, if not impossible, to get an exact idea 
of the structure of an appendage without the aid of wax 
models, of which Simmons does not say he made any use. 
'I’he last paper on the spider’s lung-book to be considered 
is that of -Jaworowski (’94), who studied Trochosa singo- 
riensis. He discovered in this species an embryonic structui e, 
which he de.scribes as an embryonic trachea, consisting of an 
ante-chamber, a trunk, and branches. 'I’he ante-chamber is 
inverted funnel-shaped, with the apex pointing upwards and 
the broad end terminated ventrally by the abdominal appen- 
dage or operculum. The sides of the ante-chamber are 
closely appressed to one anotlier (j). 56) and extended in a. 
sagittal plane (since they are seen broadways in sagittal 
sections). The pulmonary lamelhe are formed by parallel 
folds of the wall of the ante-chamber, “ the edges of the folds, 
which jut into the lumen, being more or less (figs. 1 and 2) 
undulate” (p. 62) and parallel to the surface of the operculum, 
i. e., transverse to the axis of the ante-chamber and trachea. 
According to Jaworowski’s idea, therefore, the free edges 
