KESFIRATORY ORGANS IN ARANE.E. 
37 
section (fig. 6) showing five pulmonary furrows and the other 
(fig. 5 ), although of the same age, only two such farrows. 
It is plain that the author considers that the earliest lung- 
leaves are fonned entirely within the pulmonary pit or sac 
and not on any part of the free surface of the appendage 
outside of the sac; so that, as far as the position of the 
lung-leaves in regard to the appendage at their first appear- 
ance is concerned, the author has not advanced beyond what 
was known to his predecessoi’s. Nevertheless, in the sum- 
mary at the end of the paper we find the following statement, 
that ‘Hhe lung-book of the spider (and presumably of all 
Ai’achnids which possess one) arises at first as an external 
structure upon the posterior surface of the abdominal 
appendages” (p. 219). 
If we accept the theory that the lung-books are derived 
from gill-books as indisputable, then we can say that the 
appearance of the lung-leaves on the outer or anterior wall of 
the pulmonary sac proves that this wall is morphologically 
the posterior side of the abdominal appendag’e, but we cannot 
conversely first call this wall the posterior side of the 
appendage and then say that the appearance of the hing- 
leaves upon it proves that they are formed on the posterior 
side of the appendage, as Simmons does. For if we choose 
to consider that the lung-h-oks were derived from internal 
tracheae and not from external gill-books, the pulmonary sac 
would be the trunk of a ti’achea, and no one would then call 
its outer wall the posterior wall of the appendage. Thus, if 
Simmons’ description of the early development were correct, 
then the lung-books would not arise at first as an external 
structure, but as an internal one in an invagination. 
As a matter of fact Simmons’ representations of the abdo- 
minal appendage in his figs. 5 and 6 are very misleading, as 
will appear if we refer to his fig. 10, which represents an 
entire embryo of the same age as those in figs. 5 and 6. 
Here the first abdominal appendage has its usual stumpy, 
knob-like form, and is situated on opposite sides of the 
abdomen, almost antipodal in fact, just as in Attus f loricola. 
