APPENDAGES AND NERVOUS SYSTEM OF APUS CANCRIFORMIS, 349 
On account of its possessing muscles capable of moving it 
upon the corm, the gnathobase may be distinguished from 
such outgrowths of the corm as are devoid of muscles or not 
jointed at their base. Such outgrowths or apophyses pro- 
bably are phylogenetically antecedent to outgrowths capable 
of flexion, or actually jointed at their base ; accordingly, the 
simpler early condition may be indicated by the term “lobe,” 
whilst the later flexible condition is indicated by the term 
“* arthrite.” 
Mere lobes tend in various regions of the arthropod body 
to become arthrites, e.g. the spines on the abdominal cara- 
pace of Limulus, or, again, the carapace of some Entomo- 
straca and the wings of insects. 
Further, an arthrite may be monarthrous, or, as we shall 
see exemplified in other appendages of Apus, may become 
polyarthrous. 
The four endites distal to the gnathobase are oval, leaf- 
like bodies, of which the proximal is somewhat broader than 
the others, and is, by exception in this and other appendages 
of the post-genital region, devoid of a special muscular slip, 
and therefore in the condition of a lobe instead of an arthrite. 
The three apophyses distal to it (3, 4, 5) are true arthrites, 
each being connected at its base with a muscular slip, which 
unites with its fellows to form a powerful muscle traversing 
the corm and inserted into the body wall. The arrangement 
of setze on these endites is characteristic, and is best under- 
stood by reference to the figures. 
The distal endite (6) is much larger than the preceding, 
and is attached at the point, which is practically the apex of 
the corm. It spreads both ventrally and dorsally from its 
point of attachment, so that a dorsal process may be distin- 
guished from a ventral. It is provided with a muscle dis- 
tinct from that of the other endites which traverses the 
corm. 
Next in order we come to the sub-apical lobe, which may 
be regarded either as the termination of the axis of the 
corm or as the distal lobe of its external or dorsal border. 
In the appendage under description (the first post-genital), 
the subapical lobe is exceptionally large, but it is here as 
always a lobe-—devoid of muscular supply, and not in any 
way jointed. 
Passing midward along the dorsal border of the limb, we 
come to the largest of all the outgrowths of the corm—the 
pee exite (counting the proximal as the first) the flabellum 
or fan. 
It has been usual with authors to speak of this exite as a 
