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114 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



where between gonapophyses and legs. The styH, Heymons reasserted, 

 are direct derivatives of the abdominal appendages, and occur in 

 primitive forms such as Campodea and Japyx in which gonapophyses 

 are lacking. From the abdominal limb rudiments of the embryo, Hey- 

 mons showed, are produced not only the typical styli, but also the 

 cerci, and the lateral gills of the larvae of Ephemerida and Sialis. 



Since Heymons' views are based on embryological studies they 

 deserve more attention than purely theoretical considerations. In his 

 studies of the development of the appendages of Periplaneta, Ectobia, 

 and Mantis, Heymons (1896a) observes that each limb rudiment 

 of the ninth segment is early marked by a circular constriction, which 

 divides the appendage into a broader proximal part and a slenderer 

 distal part. The proximal part flattens out and finally is incorporated 

 in the definitive sternal plate of the segment, while the distal part 

 becomes longer and slenderer and develops directly into the stylus. 

 The gonapophyses, on the other hand, Heymons claims, are secondary 

 outgrowths of the sterna in the Orthoptera. Concerning them he 

 says : " In Gryllus there can be no doubt of the nature of the 

 gonapophyses. Abdominal extremities are present in the embryo on 

 the eighth and ninth segments, but they later degenerate, and in old 

 embryos as well as in young larvae leave not the slightest rudiments. 

 It is only later, in older larvae, that the gonapophyses appear, and 

 they are therefore undoubtedly to be regarded as secondary integu- 

 mental outgrowths." Thus, according to Heymons, the stylus and 

 not the gonapophysis is the representative of the telopodite in an 

 abdominal appendage. 



It must be conceded that the facts of embryonic development do not 

 necessarily recapitulate phylogenetic evolution, since we can never 

 be sure that the early stage of an organ reproduces the primitive form 

 of that organ, and this must be particularly true of a rudimentary 

 structure. Thus, if the telopodite of a limb bearing a basal exite 

 process has long been lost, the limb rudiment in the embryo might be 

 supposed to consist of the limb basis and the accessory process, and 

 to lack the telopodite element entirely. Hence, while Heymons' 

 evidence of the nature of the styli is highly suggestive that the styli 

 are the rudiments of the telopodites, it does not demonstrate the 

 point. On the other hand, Heymons' line of reasoning concerning 

 the gonapophyses makes it seem almost certain that the genital proc- 

 esses are not the telopodites of the gonopods, but the facts of develop- 

 ment can scarcely be taken as evidence that the gonapophyses do 

 not belong to the genital appendages. It is amply proven in the Thy- 

 sanura that the gonapophyses are processes of the gonopods, and in 



