374 The American Naturalist [May, 
“ Bilaterien, ” that is for Mollusca, Worms, Myriapods, Insects 
and especially Vertebrates, than for the simpler organisms 
Protozoa, Porifera, Hydrozoa, Actinozoa, in which this ele- 
ment of symmetry is absent or more or less obscured. 
Professor Wilder has already used “ peripherad” as the 
antithesis of “centrad” and according to Schulze’s system 
peripheran could be used for the distan surface in general. 
Thus the mesenteries of the actinozoa extend peripherad from 
the principal axis or the median plane. 
It is also questionable whether a good topical classification 
of such animals as Actinozoa and Echinodermata ought not 
to recognize an intermediate region between the central and 
distal regions. There would be just as great a difficulty in 
defining a central region and a distal or peripheral one as in 
limiting the use of these terms to two regions separated by a 
third, which might be termed the extra-central with reference 
to the axis or extra-median when used with reference to the 
corresponding plane. 
(3). “Die Sympeden oder Bilaterien,” Zeugiten oder Cen- . 
trepipden of Haeckel. These bilateral bodies have three axis. 
The “ perlateral ” axis is described as “isopolar” by Schulze, 
probably in allusion to the organic similarities of its poles. 
“ Equiradial” would be equally good description on account 
of the equal lengths of the radii of the axis. The other 18 _— 
the dorso-ventral axis and is what he calls “ heteropolar : and 
this is apt to be also inequiradial. The principal axis 1$ the 
longitudinal axis, also described as “ heteropolar” and apt to 
be also inequiradial, estimating from the supposed organie 
centrum. Allin the principal axis is “ axian, ” the neighbor- 
hood is “ axial, ” the direction “axiad,” or one may slop ae 
proximal, proximad, farther from it everything is “distal,” an 
the direction away from this axis is “ distad.” 
The two ends of the principal axis are respec 
instead of “ cephalic” or “ oral ” or “ proral” (Prora, PPO”, r 
vessel) and the tail end or the other end, whether distinguish 
by a tail or not, “ caudal” instead of “ aboral.”” 
” 
tively “rostral 
ora, prow of & 
; ik ăç 
®Schulze subsequently gave his nomenclature with illustrative figures 
y ga eutsch. Zool. 
Verhandl. d. Anat. Gesellsch., May 1893, and Verhandl. d. a this last * 
Gesellsch., May 1893. In this paper and in the discussion following 
