No. 400.] SEGMENTS OF THE HEXAPOD LEG. 269 
podial forms that a series of the appendages move more or less 
in unison, and it is obvious that such rhythmic motion is better 
maintained with the articulation of a coxa and trochanter alone 
than with an additional articulation between the trochanter 
and femur. This may be a factor in accounting for the more 
pronounced fusion of the two segments in the Diplopoda. 
In 1893 Hansen! endeavored to homologize the trochanter 
of the Hexapoda with the ischiopodite in Crustacea. This 
homology was based on the supposition that the part assumed 
by him to be the trochantin? in the Cicadaria (Cicadidzx, Ful- 
X12 
Fic. 2. — Hydrophilus triangularis. Mesothoracic coxa. 
goridæ, Cixidæ, etc.) was the homologue of the coxopodite in 
Crustacea. In referring to Machilis, he has considered the 
trochantin of the prothoracic coxa as a primary segment, homol- 
ogous with the coxopodite. From comparisons, however, with 
both Chilopoda and Diplopoda, we would regard the trochantin 
rather as a specialized character of the Hexapoda, which is 
absent in the Crustacea. Homologies based upon the form of 
the segment and manner of articulation certainly appear ques- 
l Zur Morphologie der Gliedmassen und Mundtheile bei Crustaceen und 
Insecten. Zool. Anz., pp. 193-198, ppr 1893. 
2 It seems probable that Hansen has here applied the name * trochantin " to 
the antecoxal piece and trochantin ses oce 
