76 
\V. F. FUKCELL. 
origin of the trachea?, as well as of the lung-books in 
A r a n e a?. 
The origin of the tendinal or medial tracheal trunks in Ai’aneae. 
— As the pair of ventral longitudinal muscles is a very primi- 
tive structure, and must originally have been attached to the 
outer hypodermis, it follows that the tracheal nature of the 
tendinal or medial tracheal trunks must be a secondary 
character, for if this were not the case we should have to 
assume that all the ectodermal areas of attachment of the 
ventral longitudinal muscles were originally derived from 
trachese, since they are all seihally homologous, but this 
would be an absurd supposition and quite contrary to the 
facts of embryology and comparative anatomy. 
I have also already pointed out that these medial trunks 
cannot be considered as branches of the lateral ones, nor does 
the embryological evidence show that they are otherwise 
than independent metamorphosed entapophyses united at 
their base with the lateral trunks by an intertracheal fold 
and canal of communication, exactly in the same way as the 
entapophyses of the pulmonary segment are united with the 
pulmonary sacs by an iuterpulmonary fold and canal of com- 
munication. The independent nature of the tendinal trunks 
is obscured in the adults of such forms as the Attida? (fig. 
dl), owing to the partial fusion of the rudiments of the lateral 
trunks with the base of the medial ones, but it is clear 
enough in most other forms. Even in such forms as 
Segestria, Scytodes, and Palpimanus, where the enta- 
pophyses have not been converted into trachem, they remain 
attached to the smooth pedicel at the base of the lateral 
trachem (Sege stria, fig. 32) or to the spinous canal of com- 
munication uniting the two lateral trunks (Scytodes [fig. 
38], Palpimanus), and do not shift their jiosition on to the 
spinous part of these trunks. These forms, therefore, do not 
provide us with any grounds for supposing that the spinous 
parts of the medial trunks in other spiders have originated 
as outgrowths from the spiuous part of a lateral trunk. 
In fact, we have no other alternative, in view of 
