688 MR. P. R. AWATI ON THE MECHANISM 
structures articulated to the proboscis, which they took to be 
the labial palps. The palps are, therefore, in this view, separate 
from the proboscis, and do not take any part in its formation, 
the proboscis being formed by the fusion of the second maxille 
only. 
After Savigny comes Gerstfeldt (14). He elaborated this 
view as Kraepelin had done the earlier one. According to him: 
‘‘ Das erste Glied das nach Burmeister allein die Unterlippe 
darstellt, wire an das submentum und entsprache den Cardines 
der Lippenkiefer, das zweite Glied bestande aus den beiden 
Stipites und wire analog dem Mentum, das dritte und vierte 
Glieder gehérten zusammen den Endlappen der Unterlippe an und 
entsprachen entweder nur den ausseren Laden (Paraglossx) oder 
nur den unteren Laden (Ligulz), oder aber, was mir noch wahr- 
scheinlicher ist, beiden mit einander vereinigten Ladenpaaren 
zugleich.” 
Leon (29-33) has fully dealt with the question of the homo- 
logies of the proboscis. His examples are taken from the 
Belostomide. He clearly demonstrated the presence of the labial 
palps as distinct from the proboscis, and came to the following 
conclusion, after examining all the examples : 
“Hs ist ganz gleichgiiltig, in welcher Weise die Glieder der 
Scheide von einer Art zur andern, sei es als Form, Grosse, als 
Borstenanzahl, als Chitinerhebungen, etc. variieren mochten, eins 
bleibt immer constant, das die Scheide aus derselben Zahl von 
Gliedern besteht, die immer dieselbe Stellung zu einander haben 
und die vollkommen homolog sind den Bildungsgliedern des 
Labiums der beissenden Insecten.” 
In the meantime, Dr. R. Heymons (18) had published the 
result of his study of the development of certain rhynchotous 
forms. His conclusions are:—(1) the labial palps have entirely 
disappeared in the adult Rhynchota; (2) the so-called labial 
palps are secondary structures from the third segment of the 
proboscis ; they appear in the embryo but they degenerate and 
disappear in the later stages. Leon, however, does not agree 
with these conclusions. Heymons has deduced them from the 
study of the comparative embryology of these forms; while Leon 
has come to his different conclusions from the study of their — 
comparative anatomy. His conclusions are :—(1) The labial palps 
persist in the adult forms; (2) they have been discovered in 
Nepa, Ranatra, and certain Belostomide ; (3) it is not possible 
for any secondary structures to originate at the same place where 
the primary structures had been before, and to perform the same 
function as the latter. 
While the homologies of the labium were being discussed in 
Europe, a novel interpretation of the same structures was 
put forward in America by Prof. J. B. Smith (45), who had 
brought his special knowledge of the mouth-parts of Diptera to 
bear upon this question. He held that the proboscis was a part 
of the first maxille; the basal segment of the proboscis being the 
cardo ; the second, subgalea; the third and the fourth, the two 
