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315 
All adult Arachnids show clear traces of these cephalic lobes. In 
the Araneidae, Chernetidae, and Schizonotidae, they still retain the 
importance which they have in Galeodes, and though somewhat more 
disguised, occupy the whole anterior dorsal surface except when me- 
dian eyes are developed on an ocular tubercle. In Phrynus and Scor- 
pio, the cephalic lobes are very much obscured by the shoulders of the 
pedipalps, which have also moved up laterally to take part in the for- 
mation of the dorsal surface. * 
u 
Lia 
‘4 
n 
According to this interpretation of the »head« region of Arach- 
nids, the ocular tubercle, wherever developed, is a remnant of the old 
dorsal surface protruding between the cephalic lobes. This protrusion 
is very marked in the Scorpionidae, in which the ocular tubercle 
Fig. 1. Diagram of the head of Galeodes from the side. e? cephalic lobes; 
ch chelicerae; J labrum;  padipalps; 1, 2, 3, 4 the four legs. 
Fig. 2. The same from above. 
Fig. 3. Embryo of Pholcus opilionides (after Cla parèd e) showing the cepha- 
lie lobes thrown back over the dorsal surface as in Galeodes. 
seems to be forced up through the suture between the cephalic lobes. 
In the Silurian Scorpion Palaeophonus nuncius!, the remains of the 
original dorsal surface is seen as a kind of island being gradually in- 
vaded by the approximating cephalic lobes. In Galeodes again, the 
ocular tubercle shows a marked discontinuity with the surrounding 
cuticle, often (Rhax) differing in colour from the rest of the head re- 
gion. It stands up as an abrupt prominence at the anterior end of the 
median suture. This is probably the primitive position of the eyes?, 
whereas that realized in Scorpio is secondarily acquired. The shifting 
backwards of the ocular tubercle along the median suture has gone 
furthest in the genus Opisthophthalmus. 
1 On a Silurian Scorpion from Gottland. Thorell and Lindström, Stock- 
holm 1885. #1 
2 ef, Embryology of a Scorpion. Laurie, Q.J.M.S. Vol. XXXI. Fig. 38. 
