564 The Inter-Relationslups of Arthropods. [June, 
environment ; though it must be admitted that the reason why a 
terrestrial life should cause the development of these organs is 
not as easily explained as in the case of the tracheæ. In proof, 
however, of the point made, it may be stated that in those amphi- 
pods which like Gammarus and Orchestia are more or less terres- 
trial in habit, similar tubes are developed from the same portion 
of the alimentary canal, and further that their size and length is 
directly proportional to the more or less terrestrial habits of these 
forms. The same is apparently true of some of the isopods, though 
on this point our information is deficient. 
_ Another point usually emphasized is the fact that in the Crus- 
tacea a biramose condition of the appendages occurs while this — 
is not known in the “tracheates.” The studies of Lankester on 
Apus have shown how this biramose condition arose, and the fact 
that frequently it is lacking in the Crustacea would tend to indi- 
cate that it might have existed in the ancestors of the “tracheates”’ 
and have been lost in the present forms. Even more important 
is the fact that such structures are not unknown in the “ trache- 
ates.” They occur, as James Wood-Mason has shown, in the 
thysanures, and Patten has described a similar state of affairs in 
the embryos of the cockroach. _ 
So far as our present knowledge goes we can say nothing as to 
the primitive position of the antennz of hexapods ; whether they 
be processes of the procephalic lobes somewhat like those of 
Peripatus or appendages which originally belonged to the post- 
oral series and which have moved forwards to a pre-oral position 
as have the similarly named appendages of the Crustacea. In the 
former case the differences in this respect between the hexapods 
on the one hand and the Crustacea and Acerata on the other will 
be seen to be very great. If the other view prove to be the true 
one, these organs of course will have less importance from a 
taxonomic standpoint. Still the differences will be very marked. 
That the former view is correct I am inclined to believe. If we 
accept it and regard the antenne as something entirely repre- 
sented in spiders and Crustacea and then make a serial compari- 
son as before, the result is as follows: 
HEXAPODA. ACERATA, 
i oe a Chel 
u, Maxi : Pedi 
ut, Labium, Jay 
Legh Leg 11. 
Ve Leg 11. Leg lll. 
