646 PROFESSOR E, RAY LANKESTER. 
In deriving the Hexapods and Myriapods from Galeodes we 
should have to suppose the antenne of the former to arise 
de novo—a supposition which is contrary to one of the fun- 
damental principles of phylogeny, viz. that new organs do 
not arise de novo as new parts, but by the modification of 
pre-existing parts. 
Hence it seems that in any case the tracheate Arachnida 
must be left apart from the other tracheate Arthropods as 
the extreme modification of the series originating in the 
Limuloids. 
This conclusion is, however, in opposition to the view that 
the renal Malpighian tubes are of phylogenetic significance. 
It is a very striking fact that all well-developed tracheate 
Arthropoda (except Peripatus) have not only trachee as 
respiratory organs, but also have these Malpighian ceeca grow- 
ing from the proctodeum. Either the Hexapods and Myria- 
pods are closely related to the air-breathing Arachnids or 
these Malphighan ceca have, like the trachez, appeared more 
than once independently in divergent lines of the Arthropod 
family-tree. 
A minute comparative study of the structure and devyelop- 
ment of these ceca is wanting; at the same time it appears 
that certain of the Isopod Crustacea possess organs com- 
parable to them. If this be so, another possible place of 
attachment for the Hexapods and Myriapods to the Arthro- 
pod family-tree is indicated, which, on independent grounds, 
has much in its favour. Supposing that the antenne of 
Hexapods and Myriapods should prove not to be identical 
with the prostomial antenne of Cheetopods but should be 
shown by the examination of the development and structure 
of their connected nerve-ganglia to be like those of Crus- 
tacea, originally post-oral appendages, or supposing on any 
other grounds that the antenne of these forms could be 
identified with one pair of the Crustacean’s antenne, then 
it would not be difficult to conceive of such a modification of 
the post-oral appendages of an Isopod as would give the 
disposition characteristic of them in either Myriapods or 
Hexapods. 
And it is to be noted that among existing Isopods, terres- 
trial forms are known with peculiar lung-like pouches 
adapted to aérial respiration. 
A strong argument in favour of the derivation of the Hexa- 
poda from Crustacea appears at first sight to be afforded by 
the minute structure of the compound eye of the two series 
of organisms. 
Amongst all the possible points of genetic connection of 
