FIJOM EGG TO INSECT SNODGltASS 397 



pairs of legs (fig. 29, Z), but on the head there is a pair of long 

 antennae (Ant) arising from the face, and other paired organs at- 

 tached about the mouth {Md, Mx, Lb), while on the abdomen there 

 is commonly an ovipositor, or egg layer, composed of two or three 

 pairs of blades (Ovp), and near the tip a pair of slender cerci {Cer). 

 All these members arising from the ventral parts of the several body 

 regions are known collectively as the appendages. The wings (W) 

 are not appendages in the technical sense, since they arise from the 

 back and are not of the same nature as the antennae, moutli ])arts, 

 legs, and cerci. 



The appendages appear on the embrj^o soon after the segments 

 are distinguishable, and are at lirst mere swellings of the germ band, 

 forming a row of buds on each side along the lines that will later 

 be the edges of the under surface of the insect. The first and the 

 last segments never acquire appendages, but the other segments, the 

 second to the twentieth, inclusive, may have each a pair. Hence, 

 though few embr3^os have the entire possible number of appendages, 

 a " generalized " embryo would have the structure shown at B of 

 figure 14, and this may be taken as the primitive embryonic structure, 

 and probably as the ancestral one. In most insect embryos the 

 abdominal appendages are but weakly developed, or are not formed 

 at all at this stage, those that are present on the adult being devel- 

 oped at some stage after hatching. 



To follow the development of the simple embrj^onic appendages 

 into the various adult organs they become would be most interesting, 

 but it would involve a long dicussion, and the following brief state- 

 ments are all that can be given here. The first pair of appendages, 

 those of the second segment (fig. 14 A, Ant), simply elongate into 

 the antenmc of the mature insect and move forward from their orig- 

 inal lateral position to one usually near the middle of the face. The 

 appemlages of the third segment, often called the second antenme 

 {2 Ant), are at best but rudimentary organs in insects and disappear 

 as the embryo develops (B), except in one species in which they are 

 said to })ersist as small lobes in the adult. The appendages of the 

 next three segments, the segments which are added to the primitive 

 head (A, Pre) to form the head of the adult (B, H), become the 

 feeding organs, or mouth parts, of the adult. These are the man- 

 dibles (B, Md), the first maxillae {IMx), and the second maxillae 

 {'JiMx), the last uniting with each other to form the liplike labium 

 of the adult (fig. 29, Lh). The appendages of the thoracic seg- 

 ments develop into the three pairs of legs (fig. 14 B, L). The ab- 

 dominal appendages form various structures of the adult. In most 

 insects those of the first seven segments disappear ; parts of those of 

 the eighth and ninth segments form the blades of the ovipositor 

 (fig. 29, Ovj)) ; and those of the eleventh segment (or perhaps of 



