556 
AV. F. PURCELL. 
blood. This greater efficiency would account for the liiglier 
de gree of development of tlie medial trunks in many forms. 
Now out of the twenty-four families in which the medial 
entapophyses have been converted into trachemg twenty-two, 
according to Lamy’s investigations, possess tracheal systems 
consisting of four simple tubes (p. 554, text-Kg. 21) in some 
of their genera at least, while eight of these families possess 
both this simple type and more complicated types as well. 
In fact, only two very small families (G*lcobiida3 and Pro- 
didomida3) have the more complicated type ouly. And 
since the type with branched medial trunks must have been 
derived from the type with simple trunks, as the medial ones 
were originally simple entapophyses, we may fairly conclude 
that the comtnou type with four simple tubes is the primitive 
one for the entire group, and that the more complicated 
types must have been developed from the simpler types 
within each family separately and independently of similar 
complicated types in other families. This statement is in 
agreement with Lamy’s view referred to in the introduction, 
except that this author does not consider any particular type 
as more primitive than another. 
Again, it is evident that the type of trachea in which the 
entapophyses are not respiratory must be considered as more 
primitive than those in which they are respiratory, since the 
more efficient medial tracheal trunks would not be likely to 
revert to their original function after once being metamor- 
phosed. Hence the trachea? of the Fi listatida?, Sicar- 
iidte, and Palpimanidm must be looked upon as more 
primitive than those of group B with metamorphosed medial 
trunks, and it seems to me very probable that the trachea? of 
the latter group were originally derived from some such form 
as that found in Filistata (p. 553, text-tig. 20). In this 
spider the trachete are placed, according to Lamy (;02, p. 172, 
tig. 11), about midway between the spinners and the inter- 
pulmonary fold. The anterior end of each of the tracheal 
entapoj)hyses is situated near this fold, and consequently the 
segments of the longitudinal muscles between the entochon- 
