450 NATURAL SCIENCE. JUNE, 
(Ovgyia antiqua) recalls an annelid parapodium with its sete. This 
supposed difference in origin of the breathing-tubes in the two classes 
leads to a supposed corresponding difference in the origin of the - 
limbs, those of the insects being traced to the ventral series of para- 
podia of the annelid, and those of the arachnids (and also crusta- 
teans) to the dorsal series. Ingenious as this theory is, the great 
cleft which it makes between the insects and arachnids by destroying 
the homology of their appendages, seems a grave objection. The 
higher annelids have undergone too considerable a development 
along their own particular line to be safely regarded as approximating 
to the extinct ancestors of a distinct phylum. 
However, in a recent memoir, Sinclair (9g) also suggests the 
derivation of lung-sacs from tracheze rather than that of the latter 
from the former. He describes peculiar breathing-organs in the 
Scutigeride, consisting of dorsal slits opening into air-sacs, from each 
of which a number of tubes, arranged in two semicircular masses, are 
given off; these organs are believed to represent a stage between 
ordinary trachez and the lung-books of spiders, the lungs of scorpions 
representing the highest development of the series. 
But the relationship between the various kinds of breathing- 
organs depends upon the question whether the lung-bearing or 
tracheate orders of arachnids are the more primitive. In the 
scorpions, we find four pairs of lung-sacs, and the full segmentation 
of these animals has already been dwelt upon as evidence of their 
archaic nature. Moreover, while paleontology has not yet thrown 
much detailed light on the history of the arachnid groups, strong 
confirmation of this view is derived from the fact that remains of 
scorpions occur in the Silurian rocks, and that these are the oldest 
air-breathing animals of which we have certain knowledge. In the 
scorpion-spiders, and in the lower families of the true spiders, two 
pairs of lung-sacs occur, but in the higher spiders, as already 
mentioned, the hinder pair of these are replaced by trachee. Here, 
again, such knowledge of fossil spiders as we possess supports the 
view that lung-sacs preceded trachez, for while four-lunged spiders 
lived in Carboniferous times, the higher members of the group have 
only been found fossil in Tertiary formations. The comparatively 
recent orgin of the higher spiders is also suggested by a study of 
their distribution, most of the families and genera being world-wide 
in their range. Marx (10) has recently remarked that among 292 
species of spiders from the Arctic regions, none can be referred to 
special genera; and British naturalists who have read Hudson’s 
‘“‘Naturalist in La Plata” must have observed that, while the 
mammals and birds and insects described are far removed, indeed, 
from our native animals, in the chapter on spiders we are introduced 
to such familiar friends as Tetvagnatha, Zilla, Pholcus, and Avrgyroneta. 
Among the four-lunged spiders we meet with the confined and 
discontinuous distributions so characteristic of old-time groups of 
