556 
J. S. KINGSLEY. 
nothing of the change in form and function of the abdominal 
appendages. It also necessitates a change in the nomenclature 
of the regions of the Trilobite body. The head will correspond 
to the cephalothorax of Limulus, and the thorax and abdomen 
or pygidium together will equal the abdomen of the horseshoe 
crab. 
The Systematic Position of the Arachnida. 
Since 1858, when Leuckart divided the old group Articulata 
into Worms and Arthropods, and the latter group into the 
equivalents of Branchiates, not a single author, so far as I am 
aware, with the exception of Van Beneden and Lankester, has 
questioned the close association of the Arachnids with the 
Hexapods and Myriapods in a common group called either 
Insecta or Tracheata. Entirely independently of Professor 
Lankester’s papers (’77 and ’ 81 ) I came to somewhat similar 
conclusions, which may be stated as follows : — Omitting Peri- 
patus, the Arthropods should be divided into three equivalent 
groups or classes, one embracing the Crustacea, the second 
Limulus and the Arachnids, and the third the Hexapods and 
possibly the Myriapods. The last of these for convenience 
may be called Insects, the second Acerata (a modification of 
the name given by Latreille to the Arachnida alone). The 
Crustacea and Acerata are more closely allied to each other 
than either to the Insects, and the nearest representatives 
to-day of their common ancestor are Limulus and Apus. 
Before these two classes diverged the Insects had left the 
primitive Arthropod stem. 
The points of difference between the Arachnids and the 
Insects are many, those between the former group and the 
Crustaceans less in number and more readily to be considered 
as derivations of a common ancestor. These points and their 
hearings I will consider in a rapid manner beginning with the 
anterior appendages, the posterior in all of the groups showing 
too many variations to afford any decisive results. 
First, in the Insects we have antennae which are primitively 
pre-oral, and not to be homologised in position or character 
