296 INSECTA. 



front of the mouth, and that they are entirely homonomous with the other 

 trunk-limbs, and cannot therefore be traced back to the primary cephalic 

 tentacles of the Annelida.* 



Carriere (No. 13) has asserted the presence in Chalicodoma of a pre-antennal 

 limb-rudiment. According to him, the rudiment of the procephalon represents 

 a first pair of limbs, the pre-antennal rudiment the second, the antennae the 

 third, the transitory limb of the hypothetical pre-maxillary segment (p. 292) 

 the fourth, and the mandible the fifth pair of the series. These statements 

 require confirmation before we can accept them as exjfiaining the true relation- 

 ship of the series of the limbs. 



Of the limb-rudiments following the antennae, the three next 

 pairs are transformed into the jaws (mandibles, first and second 

 maxillae, Figs. 146 and 147, ind, mx v mx.^). These rudiments 

 develop early and with a complicated form in keeping with their 

 later specialisation, the mandibles appearing toothed and the maxillae 

 lobed. The second maxillae fuse together in later stages to form 

 the lower lip. The three pairs of limbs which follow these (the 

 thoracic legs, Figs. 146 and 147, p 1 , p> 2 , p B ,) exhibit a massive 

 development, the first traces of the future segmentation soon 

 becoming apparent on them. 



In the Libcllulidac., the rudiment of the second maxilla appears very large 

 in the embryo (Fig. 138, mx 2 , p. 278), so that it looks more like that of a 

 thoracic limb than like those of the other jaws. Its special development is 

 probably connected with the size attained by the lower lip (mask) of the larva 

 which proceeds from it (p. 359). 



With regard to the order of appearance of the different limbs, our knowledge 

 is as yet somewhat incomplete. Here also we find repeatedly that the general 

 order of development is, according to the ontogenetic law, from before back- 

 ward. In many forms the antennal rudiments seem to be the first to appear, 

 while the maxillary rudiments and those of the legs all develop simultaneously, 

 but somewhat later than the antennae. This is the case in Hydrophilus, 

 Melolontha, and Stenobothrus. In Lina, according to Graber (No. 30), the 

 mandibles precede the antennae. Among the Libcllulidac, according to Brandt 

 (No. 7), the rudiments of the thoracic limbs appear first, then those of the 

 maxillae, and only later those of the antennae. In those Insects whose larvae 

 are limbless, on the contrary, the rudiments of the thoracic limbs appear late 

 and in an arrested condition (Apis and Chalicodoma), or are altogether sup- 

 pressed (Muscidac). In the first case, the limb-rudiments degenerate before 

 the larva hatches. It would be interesting to trace the relation of these 

 degenerating rudiments to the imaginal discs of the thoracic limbs that develop 

 later, concerning which, as far as we know, no statements have been published. t 



* From this point of view, the malformation observed by Kriechbaumer in 

 Bombus (Entomol. Nachr., Jg. xv.) is not without interest ; an antenna was by 

 this author found deformed so that it resembled a leg, and at its end carried two 

 well-developed claws. See Bateson, Materials for the Study of Variation, p. 146. 



t [BtJRGER (No. II.) finds in Chalicodoma that the thoracic appendages of the 

 embryo flatten out and their hypodermal cell-layer thickens and becomes the 

 imaginal discs of the thoracic limbs of the adult. — Ed.] 



