18 
Psyche 
[ March 
from that of Tremex in outline and absence of dorsal 
grooves. The claws are simple and the basipulvilli small. 
The orbicula, ; a small dorsal sclerite, is not shown in this 
view but this plate is variable throughout the Hymenop- 
tera and together with the planta and unguitractor should 
prove valuable in studying the inter-relations within the 
order. As with the Diptera, it seems probable that further 
study of primitive types will be of phylogenetic value for 
the variety of structures does provide a wealth of material 
to work on. 
Summary. 
Without losing sight of the fact that only a few speci- 
mens selected at random from each order are studied, the 
evidence thus secured does seem to point out certain ten- 
tative hypotheses to be further investigated. 
1. That the planta occurs in most of the insectan orders 
as a sclerotized area of the membrane just distal to the un- 
guitractor and that this structure is homologous throughout 
by position, ie., its relation to the unguitractor, basipulvilli 
and claws. The presence of one or more setae may be a 
distinguishing feature; note the condition in cursorial Or- 
thoptera and Hymenoptera. The degree of sclerotization 
is quite variable for in some cases the planta is almost en- 
tirely membranous while in others it forms a heavy plate. 
2. That the empodium is a highly modified planta. No 
planta was found (in specimens so far observed) in the 
orders Diptera, Hemiptera, Coleoptera and Dermaptera but 
an empodium is present in at least some representatives of 
all these orders. On the other hand, wherever a planta oc- 
curs an empodium has not yet been observed. The condi- 
tion of the planta in Gryllotalpa and Psalis, where it is 
closely associated with the unguitractor, illustrates how 
difficult an attempt to distinguish between these two struc- 
tures may be. Comparison of Gryllotalpa with other Or- 
thopteroids leaves but little doubt but what the part re- 
ferred to is a planta even though numerous setae are pres- 
ent, for such appendages also occur on the plantae of cur- 
sorial Orthoptera and Hymenoptera. The occurrence of pa- 
rempodia, which are really setae, on the empodia of Coleop- 
