88 
W. F. rOL’CELL. 
are represented by external appendages in the adult scor- 
pion, and the two anterior pairs of lung-books in the latter by 
external appendages in the adult spider. Now I cannot 
imagine that the pectines of scorpions could have been 
derived from appendages which had already sunk into the 
abdomen and been converted into lung-books, and the con- 
verse, that these external organs, after having lost their 
branchial nature and acquired new functions could ever have 
been converted in lung-books, is equally improbable. I con- 
sider, therefore, that the lung-books of the scorpions 
and those of the spiders must have been derived 
from branchiate appendages quite independently 
of each other, a ndt hat the terrestrial Arachnids are 
not monophyletic but must have bad at least a 
diphyletic origin from primitive aquatic Arachnids 
with six pairs of abdominal branchiate appendages 
on the eighth to thirteenth somites.^ 
Laurie (’93) has expressed a similar opinion but based on 
palaeontological grounds, that the lung-books in scorpions 
arose independently of those in other Arachnids. 
(3) Pedipalpi. — It has been recently shown by Schimke- 
witsch (:06) that in the embryo of Thelyphonus the lung- 
books belong to the second and third abdominal somites 
(p. 43), while the genital opening is found between these two 
segments (pp. G3, 64), that is to say, exactly as in the 
A r a n e ae .- 
’ It is interesting to note in this connection that Schinikewitsch 
('94, p. 207) discovered in the embryos of a scorpion on each side on the 
genital opercnlum three to four teeth (Warzen, Km., fig. 12) which were 
formed on tlie same plan as those of the j^ectines b\it vanished again 
before birth. Schimkewitsch thinks it veiy probable that the genital 
oijercnlum was once a sense organ like the pectines, and asks whether 
both were not once gills f 
2 Hansen ('83, p. 105) had previously pointed out that in Thely- 
2 )honus the first abdominal sternite should l)e sought for in the small 
sclerite at the anterior end of the abdomen, so that the large anterior 
sternite, which covers the genital ojjening and the first 2 >air of lung- 
books, would, according to Hansen, belong to the second abdominal 
