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J. S. KINGS LEY. 
perforate the ventral plates, as also in the diplopod Myriapods. 
In the Hexapods and the chilopodous Myriapods the stigmata 
are placed outside these plates. These differences in position 
of the external openings may indicate a separate origin in all 
these groups, especially when we consider Sedgwick’s specula- 
tions (’ 84 ) on the origin of tracheae. Again, it should be 
noticed that no traces of cephalothoracic stigmata or tracheae 
occur in the Spiders. 
One objection to the separation of the Hexapods and Arach- 
nids, and the closer connection of the latter with the Crustacea, 
lies in the fact that biramose appendages are characteristic 
of the branchiate and simple of the tracheate Arthropods. 
This, however, may be regarded in two lights. In the an- 
cestral Arthropod both exopodite and endopodite may have 
been present, and both branches may have been retained in the 
aquatic and only one in the terrestrial forms, or the ancestor 
may have had broad and flattened but unbranched appendages 
which have been variously differentiated in different groups. 
There are several facts in favor of either of these views, 
though the evidence presented by Apus, together with many 
other points render the latter the more probable. To mention 
one or two of these : Apus is by nearly all morphologists 
regarded as the most ancestral type of Crustacea. Its 
members (Lankester, ’ 81 a ) are broad and flattened plates 
bearing typically six internal and two external lobes, but 
studying the adult alone no one would ever arive at the idea of 
exopodite, endopodite, and epipodite. In the Nauplius stage, 
in the second and third appendages, a biramose condition 
exists. This is, however, to be regarded as secondary in its 
nature, just as is the Nauplius itself. In the maxillae of forms 
even as high as Decapods, this lamellar condition persists, and 
all attempts to trace the homologies of exopodite and endo- 
podite meet with but partial success. 
The evidence on the other side is fragmentary. Croneberg 
(’ 80 , P l. xvi, figs. 14 — 16) describes and figures an embryo 
Arachnid (Dendryphantes) in which the pedipalpi are distinctly 
bifid at the tip. This, however, has never, so far as I am 
