150 ENTOMOLOGICAL SOCIETY 



formed of two segments as are the meso- and metathorax. One 

 will see that this is probable by a glance at the figure of a Litho- 

 bius (Plate I, fig. i). Many insects show a transverse groove 

 on the pronotum. It is seen that the spiracles of the small 

 segments have disappeared in Lithobius. This has a direct bear 

 ing on the question, if it be true (as the best evidence seems to 

 show) that the wings of insects originate from rudimentary 

 spiracles. Since there are not in the lowest Chilopod any spir 

 acles on the first segment, this will explain why there have been 

 no prothoracic wings in insects. If we look again at a Lithobius 

 (Plate I, fig. i) we notice that behind the thorax is a segment 

 not followed by a smaller one. This will become the median 

 segment of insects, in some forms united to the thorax. 



Are the abdominal segments of insects compound? I do not 

 know of positive evidence, but in looking at Lithobius one would 

 think that the abdominal segments were also compound. In many 

 insects there are indications of transverse division on some of the 

 abdominal segments. Still one cannot argue too literally from 

 Lithobius, for Lithobius is not the ancestor of insects but only 

 closely related thereto. 



If we compare the head end of the lower and higher Chilopods 

 we notice that there has been an increase in the size of the poison- 

 claw, and a more or less definite coalescence with the head. It 

 would seem, therefore, that in insects a more complete coalescence 

 has been accomplished. And it is so. The Chilopod (Plate I, 

 figs, i, 5, 6, 8) has a pair of mandibles ; a lip with jointed lobes 

 each side ; a pair of slender jointed appendages, sometimes called 

 maxillae ; and the poison-claws overlapping all. What has 

 become of these parts in insects? If we examine the larva of 

 a Perlid (Plate I, figs. 2, 4), we see mandibles, lip with lobes 

 or palpus, and a complicated maxilla. In side view, this looks 

 much like the poison-claw, and it is. In some Perlid larvas, one 

 can, with a little care, separate the maxilla into two separate and 

 independent structures, without rupturing the teguments. The 

 inner part is the palpus, with its own basal joints, normally con 

 cealed by the stipes and cardo. The outer and larger part is the 

 old poison-claw, now galea and lacinia. In most insects the 

 pressure of the former poison-claw against the palpus has resulted 

 in a coalescence and twisting of parts. However, in many insects 

 (Carabidae, etc.), the galea is divided into two segments, thus 

 showing that it represents an appendage as well as the palpus. 

 The lacinia, I should guess, is developed from a spur at the base 

 of a joint. A similar articulated piece is found in the mandibles 

 of some beetles (as Cetonidaa). Thus I believe that the maxilla? 

 of insects represent two pairs of appendages fused together at 

 base ; and that each segment of the insect thorax is composed of 

 two primitive segments. 



