90 
W. F. PUECELL. 
which are totally different from mine, accordingly divides 
the Arachnida into two snb-classes, viz. (1) Ctenophora^ 
for the scorpions, and (2) Lipoctena for the remaining 
terrestrial orders. Burner (:02, p. 459) in his paper on the 
segmientation and general classification of the Arachnida, 
accepts this subdivision, bnt on other grounds, viz., on account 
of the difference in the number of the segments of the meso- 
and metasoma which appear to exist between the Scorpiones 
and the Lipoctena. Bdrner, however, considers tha.t both 
Scorpiones and Lipoctena must have been derived from 
a common ancestral group provided witii at least five pairs 
of lung-books (pp. 459 and 463), but the difficulty (in my 
opinion almost an impossibility) of deriving a lung-book from 
a pectine, or vice versa, does not seem to have occurred to 
him. 
The question of the conversion of a sunken-in lung-book 
into the external spinners of the Aranem would also present 
difficulties, but these do not appear to me nearly so great as 
in the case of the pectines, because the reconversion of the 
lung-septa (lamellae) into external gill-like organs is not 
involved. 1 have, however, already pointed out that no 
trace of a lateral proliferation, corresponding to that of 
the pulmonary and tracheal sacs, is found in the embryo of 
Attus floricola, the entire post-appendicular invagination 
becoming the entapophysis in these two segments. Moreover, 
the spinning glands appear at quite an early stage (stage 5, 
■sp. g., fig. 6) at the apex of the appendages, which always 
remain recognisable as such to the end of the development. 
In fact, they have every appearance of having been directly 
develo))ed into spinning organs from external appendages 
which were not sunken into the body, and, therefore, not 
lung-books. 
So far as our knowledge goes, therefore, we may 
say that there is no evidence of any sort to indicate 
that the spinners of the Aranem were derived from 
* For which word the term Cteidophora lias been substituted by 
Bonier (:02, p. 4b5). 
