522 
AV. F. PURCELL. 
although it resembles the Aranem verae and not the 
Theraphosae in all other respects, nevertheless, has the 
tracheae replaced by a second pair of lung-books. 
Neither of these arguments, however, wan-ant the conclu- 
sion that Lamy has drawn from them, since both cases may 
be readily explained, even when we assume that the lung- 
books were in all cases the primitive organ and that the 
tracheae were derived from them. Lamy’s assumption that 
the Dysderidae and the Caponiidae are equally primitive 
is certainly incorrect, since, as I shall presently show, the 
Caponiidae differ from the Dysderidae, as well as from all 
other spiders (so far as I know), in several important anato- 
mical characters. They are in fact, in these respects, a 
highly-specialised group, compared with which the Dys- 
deridae are much more primitive. But even if these two 
families were equally primitive they are by no means the 
most primitive spiders, the vast host of mygalomorphous 
forms being all more primitive than they and all provided 
with lung-books only. Moreover, the highly-developed 
tracheae of the D3’sderid£e, which present no obvious resem- 
blance to lung-books, do not so sti’ongly resemble the anterior 
trachem of the Caponiidae as Lamy makes out, since these 
latter are very similar to the lung-books of a Dysderid. In 
fact, these anterior tracheae may be most readil}^ explained, 
as I shall presently show, as lung-books which have been 
transformed into tracheae more recently than those of the 
second pair and which have retained the primitive shape more 
nearly than has been the case with the tracheae of any other 
Arachnid known. They have evidently been evolved out of 
a few-leaved lung-book like that of a D\^sderid, and their 
presence merel}’ proves that tracheae have been evolved out of 
lung-books within the Aranefe at least on two occasions, but 
it does not prove that the tracheae and lung-books are equally 
primitive. 
Similarly, the presence of a second pair of lung-books in 
the Hypochilidae may be quite readily explained by 
assuming that this family is an arachnomorphous form in 
