1893.] Entomology. 401 
has become of the second maxille and the maxillipeds? The maxilla 
of insects is composed of three portions, the palpus, the galea, and the 
lacinia with the basal joints. If now we look at a Perlid larva (the 
lowest winged insect) the secret lies revealed; the basal joints of the 
maxillipeds have united to form the sub-mentum, the remaining joints 
by their pressure have united to the basal joints of the maxilla. Yet 
in the Perlid larva the union is not complete and one can plainly see 
that the palpiger is not articulated to the stipes, but has basal joints 
which are concealed by the stipes and the two parts of the cardo. So 
that the maxill of insects is equal to the first maxille of Chilopods 
plus the maxillipeds. The labium of insects appears to be the same 
as the second maxille of Chilopods, the mentum being the united 
basal’ joints. ; 
I would also call attention to the steady tendency observable in 
Chilopods toward the union of certain thoracic segments. In the lower 
Chilopods (Geophilus) the segments are all of about equal size, and 
each one bears a spiracle. A little higher, in Scolopocryptops, we see 
that there are two kinds of segments, the large with spiracles, the small 
without them. Segments 2, 4 and 6 are small, the 7th and 8th both 
large, after that every other one is small. In Lithobius the process is 
continued still further, the small being smaller, the large larger. In 
Scutigera (the highest Chilopod) the dorsal scutæ of the small segments 
become united to the larger ones, so that seen from above, the first 
scuta (prothorax) covers one pair of legs, the second scuta (mesothorax) 
covers two pairs, the third scuta (metathorax) covers two pairs, and 
the fourth scuta covering three pairs of legs. Therefore I conceive 
that the mesothorax and metathorax of insects are each composed of 
two segments. This would appear quite probable if one but look at a 
grasshopper; but there exists greater proof. Machilis (a common 
Thysanuran) has on each abdominal segment a pair of small append- 
ages, which have been recognized as representing legs, but the meso- 
and metathorax also bear these appendages beside the normal legs ; 
hence if these appendages represent legs the meso- and metathorax of 
Machilis must be compound segments. It is possible that each abdom- 
inal segment is compound, but I hardly think this probable, since the 
first abdominal segment of insects, which is very small, appears to 
represent the small sixth segment of Scutigera. If this theory of the 
insect thorax be true, the thorax consists of five segments, segments 
one, three, and five bearing legs, segments two and four bearing wings. 
Narman Banks, Sea Cliff, N. J. 
27 
