LIMULUS AN ARACHNID. 645 
containing lamelligerous appendages of the Scorpion are not 
new organs, but the modified and adapted blood-containing 
appendages of a Limuloid ancestor. 
The relationship of the groups of Arachnida to one 
another thus suggested may be best indicated by means of 
a genealogical tree (see last page). I have also drawn up the 
names and arrangement of groups suggested in a tabular form. 
I have further thrown into the form of a genealogical tree 
the conclusions to which I am led in reference to the relation- 
ship to one another of Peripatus, the Crustacea, and the 
Arachnida. 
In this pedigree of the Arthropoda no place is assigned to 
the two great tracheate groups of Insecta Hexapoda and 
Insecta Myriapoda. In the present state of knowledge it 
appears to be impossible to assign to either of them one posi- 
tion rather than another. We have not even sufficient 
ground for concluding that they are closely related to one 
another. The antennz of Hexapods and of Myriapods may 
be, as probably are those of Peripatus, non-appendicular 
prostomial antenne, which would be, in addition to the 
presence of tracheze, a reason for considering both to have 
been developed from such a form as Peripatus. On the 
other hand, possibly only the Myriapoda are derived from 
Peripatus-like ancestry, and, probably enough, neither 
one nor the other. It seems to be in the highest degree 
probable, and is not difficult of admission, that there is no 
such a group to be recognised as the Tracheata. Trachez 
have probably developed independently in Peripatus and in 
the Insecta, and again in the Arachnida. Nevertheless, the 
view is capable of being defended that all tracheate Arthro- 
poda have a common tracheate ancestor ; in which case it 
will be necessary to derive the Insects, the Myriapods, and, 
to be consistent, Peripatus also, from the tracheate Arach- 
nida, through such a form as Galeodes. The derivation of 
Galeodes through the Scorpions, from the branchiate Arach- 
nida, is, relatively speaking, a well-grounded conclusion ; 
and if trachee are to have but one starting-point, it is of 
necessity here that we must look for it. 
Insuperable difficulties are, however, found in the deriva- 
tion of Hexapoda from Galeodes, in spite of curious homo- 
plastic agreements between the two. Such a difficulty is 
the absence of appendages corresponding to the antenne of 
Insects in Galeodes, and in the whole line of its Arachnidan 
ancestry, which absence has to be recognised if the pincers 
of Galeodes are identified with the mandibles of an Insect.’ 
1 I do not admit the truth of this identification. 
VOL, XXI,—-NEW SER. UU 
