88 
Wisconsin Academy of Sciences , Arts and Letters . 
because I believe, in contradiction to Graber, that there is nothing in the 
structure or evolution of the pleuropodia which throws any light whatever 
on the mooted question. 
These organs may be turned to quite as good account by the advocates of 
homopody as by those who accept Graber's views. Supposing the Diptera 
were the only order of insects of which we had any knowledge, should we 
be justified in asserting that the halteres which now function as sense 
organs according to LeucJcart and Lee, had never functioned as true wings ? 
Certainly not. No entomologist doubts that the immediate ancestors of 
the Diptera were true insects and that they were provided with two pairs 
of perfect wings. It seems to me that the advocates of homopody may 
logically maintain that the pleuropodia present a strictly analogous case. 
These organs originate as appendages homologous with the thoracic legs 
though they subsequently differentiate into organs of problematic though 
certainly not ambulatory function. Why might not the pleuropodia have 
been true ambulatory appendages in ancestral forms no more remote from 
the living or even Palaeozoic Ortlioptera than some four-winged insects are 
from the Diptera ? * 
PART FIRST. 
Blatta ( Pliyllodromia) cjermanica. L. 
(Plate I, Figs. 1-9.) 
The appendages of the embryo Blatta begin to appear on the tenth day 
from the formation of the polar globules. The antennae and the three pairs 
of thoracic limbs are the first to rise from the ectoderm of the hammer¬ 
shaped embryo. By the eleventh day the three pairs of oral and several 
* A similar argument may be advanced in the case of the hamulate halteres of the male 
Coccidce. Of deeper interest in this connection, however, are two facts recorded by 
Schioedte (De Metamorphosi Eleutheratorum Observationes, Kopenhagen, 1861-1883) con¬ 
cerning larval Scarabceidce and Lucanidce. In the larvae of most species belonging to 
these families the metathoracic legs are as long as or a little longer than the meso- and 
pro thoracic pairs. The larval Geotrypes stercorarius, L., however, has the hind legs re¬ 
duced to only half the length of the anterior pairs. (Plate XVI, Fig. 1.) In the larval 
Passalus cornutus , Fabr. the hind legs are so far reduced as to be represented by a pair 
of small rudiments only. “ Pedes tertii paris valde deminuti Geotrypoe, Passalo, completi 
Geotrypce, femoribus, tibiis, ungulis carentes Passalo." It is interesting to note that the 
rudiments in Passalus, as shown in Schioedtes 1 Figure (Plate XVIII, Fig. 12) are placed very 
near and somewhat pleurad to the bases of the median legs. The position thus assumed 
by the atrophied hind legs in respect of the median pair is exactly the same as that 
assumed in insect embryos by the pleuropodia in respect of the hind or metathoracic pair. 
The possibly unique, and certainly anomalous reduction of the hind legs in the larval 
Geotrypes and Passalus is well suited to show what striking changes may occur in the 
appendages within the limits of a single suborder of insects. This reduction, which is a 
purely larval character, since the imagines have hind legs of the usual size and structure, 
has very probably taken place within comparatively recent times. 
