46 EMBRYOLOGY OF INSECTS AND MYRIAPODS 



Polypody finds expression in the development of appendages that 

 may appear on all abdominal segments except the telson. In the 

 myriapods they are segmented and functional; in insects they are usually 

 reduced or lacking, though in the embryos anlagen of as many as 1 1 pairs 

 may be found with corresponding metameres and nerve ganglia. Among 

 Apterygotes abdominal appendages are found in postembryonic stages 

 though modified in function, as are also some posterior appendages of 

 certain Orthoptera and other primitive pterygotes. The prolegs of the 

 larvae of Lepidoptera and Tenthredinidae, generally regarded as serially 

 homologous with the thoracic legs, are well developed in the embryos. 

 In the case of the embryos of the Lepidoptera the appendages appear on 

 segments one to ten, but later they persist only on segments 3 to 6 and 10, 

 in the more typical forms (Eastham, 1930; Friedmann, 1934; et ah). 



Appendage rudiments are commonly present in the Orthoptera on all 

 the abdominal somites of the embryo, but in the male those on somites 

 anterior to the ninth disappear before hatching. The appendages of the 

 ninth segment of the male, however, are retained in many families as a 

 pair of small, nonmusculated styli borne on the posterior margin of the 

 definitive ninth sternal plate, their coxopodites supposedly in most 

 cases being incorporated in the sternal plate. According to Else (1934) 

 the embryonic appendages of the ninth abdominal segment of the male 

 of Melanoplus differentialis merge completely with the posterolateral 

 parts of the primitive sternum of this segment, even the styli being thus 

 obliterated in Acrididae. It is only in the Grylloblattidae that the ninth- 

 segment appendages retain a two-segmented structure, the coxopodites 

 being here large, free lobes bearing styli. According to Else appendage 

 rudiments of the tenth segment in Melanoplus persist and continue their 

 migration toward the median line until they take a position at the sides 

 of the point where the ejaculatory duct invagination is being formed. 

 Here they grow out into lobes that unite about the mouth of the duct 

 and eventually form the complex phalhc organ of the adult which con- 

 tains the gonopore. According to Wheeler (1893) the embryonic tenth 

 appendage rudiment in the male of Conocephalus, after the ampullae have 

 withdrawn from them, disappear. Embryonic appendages of the tenth 

 segment are retained as larval "legs" in the Neuroptera, Trichoptera, 

 Lepidoptera, and the lower Hymenoptera. 



Regarding the homologies of the appendages of the abdominal seg- 

 ments in the Apterygota and the primitive Pterygota it must be admitted 

 that in the embryo the outgrowths of the body appear so much alike that 

 their similarity offers but little proof of their identity. Whether the part 

 that develops into an unsegmented stylus or the valve of an ovipositor 

 (jr a clasper represents a reduced abdominal leg or only an appendage of a 

 completely obUterated leg is difficult to say. 



