22 TEXT-BOOK OF ENTOMOLOGY 



progoneate myriopods, which have retained the primitive feature of 

 double sexual outlets. It is more probable that the Symphyla were 

 the descendants of these polypodous forms. Certainly Scolopen- 

 drella is the only extant arthropod which, with the sole exception 

 of the anteriorly situated genital opening, fulfils the conditions 

 required of an ancestor of Thysanura, and through them of the 

 winged insects. No one has been so bold as to suggest the deriva- 

 tion of insects from either diplopods or chilopods, while their origin 

 from a form similar to Scolopendrella seems not improbable. Yet 

 Uzel has very recently discovered that Campodea develops in some 

 respects like Geophilus, the primitive band sinking in its middle into 

 the yolk, with other features as in chilopods. 1 The retention of a 

 double sexual opening in the diplopods is paralleled by the case of 

 Limulus with its double or paired sexual outlets, opening in a pair 

 of papillae, as compared with what are regarded as the general- 

 ized or more primitive Crustacea, which have an unpaired sexual 

 opening. 



The following summary of the structural features of the Sym- 

 phyla, as represented by Scolopendrella, is based mainly on the 

 works of Grassi, Haase, and Schmidt, with observations of my own. 



Diagnostic or essential characters of Symphyla. --Head shaped as 

 in Thysanura (Cinura), with the Y-shaped tergal suture, ivhich occurs 

 commonly in insects (Thysanura, Collembola, Dermaptera, Orthoptera, 

 Platyptera, Neuroptera, etc.), but is wanting in Myriopoda (Diplopoda 

 and Chilopoda) ; antenna^ 2 unlike those of Myriopoda in being very long, 

 slender, and moniUform. Clypeus distinct. Labrum emarginate, with 

 six converging teeth. Mandibles 2-jointed, consisting of a vestigial 

 stipes and distal or molar joint, the latter ivith eight teeth. First max- 

 illce, with an outer and inner mala situated on a well-developed stipes; 

 ivith a minute, 1-jointed palpus. Second pair of maxilhe: each form- 

 ing two oblong flat pieces, median sutures distinct, with no palpi; these 

 pieces are toothed in front, and appear to be homologous with the two 



1 Zoologische Anzeiger, Bd. xx, 1897, pp. 125 and 120. He also states that Cam- 

 podea resembles the myriopods, especially Geophilus, in the primitive band at first 

 lying on the surface of the yolk, and in the absence of an amniotic cavity ; also before 

 hatching the abdomen is pressed against the thorax, as in myriopods. 



2 " Scolopendrella has very remarkable antenna) ; they may be compared each to 

 a series of glass cups strung upon a delicate hyaline and extensible rod of uniform 

 thickness throughout ; so that, like the body of the creature, they shrink enormously 

 when the animal is irritated or thrown into alcohol, and they then possess scarcely 

 two-thirds the length they have in the fully extended condition, their cup-like joints 

 being drawn close together, one within the other. Peripatus, Japyx, many (if not 

 all) Homoptera, and the S. Asiatic relatives of our common Glomeris have all more 

 or less extensible antennae." (Wood-Mason, Trans. Ent. Soc., London, 1879, 

 p. 155.) 



