Paleocampa, Meek and Worthen. 293 
sanura. Ryder suggests for it an independent place between 
the Myriopoda and Thysanura, under the name Symphyla. 
Packard, with better reason, would place it within the Thy- 
sanura, under which head he would also include the Col- 
lembola and Thysanura proper, or Cinura, as he terms them. 
Scolopendrella, as these authors point out, differs from the 
Chilopoda in that the appendages of the segment behind that 
furnishing the mouth-parts proper do not serve as auxiliary 
organs for manducation, but are developed, like those of the 
succeeding segments, as legs, while the mouth-parts resemble 
those of Thysanura, and differ from those of Chilopoda: 
indeed the whole head is decidedly thysanuriform, the legs 
are provided with a pair of claws, and the terminal segment 
bears a pair of caudal stylets with a special function. Besides 
these points, the possession of a collophore is distinctively 
thysanuran ; and the position of the stigmata, between the legs, 
is different from the position they uniformly maintain in 
Chilopoda, while it only adds to the great irregularity of place 
seen in Thysanura. On the other hand, the identity of 
form in the thoracic and abdominal segments, the full de- 
velopment, upon the abdominal segments, of jointed legs like 
those of the thoracic segments, and the occasional alternation 
of leg-bearing and apodal segments in the abdomen, are stri- 
king marks of its real affinity to the chilopods. Abdominal 
appendages, homologous with legs, but unjointed, do, how- 
ever, occur in Thysanura to a greater degree than in other 
hexapods, so that we can hardly refuse to admit these poly- 
podous creatures as lowest members of the subclass of insects 
proper, although they are the only non-hexapodal type. 
Now the separation of the head and its appendages from 
those of the next succeeding segment distinguishes Palao- 
campa from the Chilopods in the same way as it does Scolo- 
pendrella ; so, too, the segments behind the head in Pulco- 
campa and Scolopendrella, alone of all arthropods in which the 
head is thus clearly separated, agree in showing no distinction 
whatever between what may be looked upon as thoracic and 
what as abdominal, whether in the form of the segment itself 
or in the appendages of the segments. These are certainly 
fundamental points ; but when we have mentioned them we 
have reached the end of all possible affinities or points of re- 
semblance, unless we may consider the minute structure of the 
rods in the fascicles of Paleocampa paralleled by the well- 
known delicacy of organization of the scales in other Thysa- 
nura, though they do not exist in Scolopendrella. The limited 
number of abdominal segments might be locked upon as a 
further point, were it not that the number is even less than 
