80 
W. F. PURCELL. 
abdominal appendages, on the posterior side of which were a 
number of separate tracheje arranged in a row, and that these 
appendages were sunk into the body in later forms. The 
tracheated appendages of such an ancestral form would, in 
fact, be very similar to one of the transitional stages which 
Kingsley assumes for his theory of the origin of lung-books 
from gills (p. 27), but it would be totally different from 
anything actually found in the tracheal system of existing 
spiders. 
F rom purely embryo logical considerations, there- 
fore, and quite apart from the branchial theory of 
the origin of the lung-books, we have to assume that 
the pair of lateral branches of the tracheae of the 
ninth somite in Dipneumonous spiders must have 
been derived from the pulmonary sac and not the 
reverse. This conclusion is, moreover, strongly confirmed 
by the fact that the Tetrapneumonous spiders, and particularly 
the remarkable genus Liphistius, are more primitive in their 
other characters than are the Tracheate spiders. 
The origin of the secondary tracheal tubules. — The third 
question is the nature of the tracheal branchlets, those fine 
tubules {tr. tuh., fig. 31) given off by the main trunks in 
certain forms (Attidte, Dysderidoe, Argyroneta, etc.). 
It is usual to consider these as homologous with the saccules 
of the lung-books, whatever view ^ may be taken of the origin 
of the latter. I think, however, that this homology is, for the 
most part, erroneous. 
Since the pulmonary saccules occur only on the anterior 
side of the pulmonary sac, we should expect to find the 
tracheal tubules on the corresponding surface of the lateral 
tracheal trunks, but this is by no means the case.” Thus, in 
' Except, however, Jaworowski and Beniard. 
- In the remarkable anterior paii‘ of trachea; of the Apneumonons 
Family Caponiidse, described and figured in Simon (‘Hist. Nat. 
Araign.,' 2e cd., i. pt. ii, pp. 326, 327, figs. 294 and 295, 1893) after 
Bertkaii, the tubtiles are nearly all placed, however, on the anterior side 
of an oval ante-chamber, and here, no doubt, do correspond to pulmo- 
