1894.] ; The Classification of the Arthropoda. 121 
Fernald, has approached the subject from the standpoint of 
Hexapod morphology. He gives (90) a phylogenetic tree in 
which two main trunks arise from the primitive unsegmented 
worm. One of these embraces the Annelids and Peripatus, 
the other includes the Arthropods proper. This latter branches 
into the Hexapods and the Crustacea, the. Arachnids and 
Limulus being represented as offshoots from the main Crus- 
tacean line. The origin of the Myriapods is left in doubt, 
but of the two divisions the Chilopods are represented as an 
offshoot from the Diplopod stem. 
Richard Hertwig (92) adopts the following scheme : 
Branch Arthropoda. 
I Sub-Phylum, I Class, Crustacea. 
1 Sub-Class, Entomostraca, containg as regular mem- 
' bers the Orders: I, Copepoda; II, Branchiopoda; III, 
Ostracoda; IV, Cirripedia ; and, as “Anhangen,” V, 
Xiphosura; VI, Trilobite; VII, Gigantostraca. 
II Sub-Class, Malacostraca. 
II Class, Onychophora. 
III Class, Myriapoda. 
IV Class, Arachnoida (including Pantopoda as an “An- 
hang”). 
V Class, Hexapoda. 
Lastly, von Kennel, whose studies on Peripatus entitle his 
views on Arthropod taxonomy to a hearing, denies (93) the 
validity of the group Arthropoda, claiming that those features 
which would seem to unite the Tracheata and Branchiata are 
either superficial or are common to the whole series of meta- 
meric Invertebrata. He places the Xiphosura among the 
Crustacea, apparently regarding them as equivalent to the rest 
of the group. The Tracheata are divided into three sub-classes, 
Myriapoda, Hexapoda and Arachnoida, the relationships of 
Tardigrada and the Pycnogonida being regarded as uncertain. 
My own views, as stated in my last paper on Limulus, have 
not undergone any extensive modification, although the tab- 
ular statement has undergone some slight changes. Chief of 
these is the transfer of the Trilobite from a position of uncer- 
tainity to a more close union with the true Crustacea, a matter 
