u 



TIIK nATUACHIA OF NORTH AMERICA. 



247 



^iT' 



The presence or absciutc of maxillary teeth was formerly regarded by 

 the author, after Diimeril and l>il»roii, as of primary value in the defini- 

 tion of the suborders. On aeeount of tiie absence of teeth, a division 

 Ibilbniformia was distin<;nishe<l from tiie Ai'eifera; and the tooth-bear- 

 injij Fermisternia weri^ called Uaniformia. I, however, now follow Bou- 

 lenger in droppinjj thes(^ divisions, since the absen<;e of teeth is some 

 times of little systematica sijiiiilicance. 



In the ar(!ilerous type (»f scapidai' arch the opjiosite halves are capable 

 of movements wliiiili contract or expand the capacity of tin' thorax; in 

 the Firmisternia the opposite halves abut afj;ainst ea<;h other soas to be 

 incapable: ot movement, thus preservinj; the siz(^ of the thora(!ic cavity. 

 This arran<j;enu-nt has an important bearin<:°on the comtbrt, and perha|is 

 health, of the female wiiile in connection witli the male. The embrj'.i;eof 

 the foreleji'sof the lattt'r behind t be axilla* of tiM^fbrtner is very energetic, 

 and is maintained by various structural aids. Thus in man.v spc-.;ies the 

 inaU's develop rough and even spinous horny plates on the inm?r sujte- 

 ricu' side of the tiiumb, which presses against the thorax of the female. 



Th(t iirmisternial stru<-ture is a mo<iilication of the arciferous, which 

 comes later in the iiistoiy of growth, and probably in geological time. 

 During the eaily stages the Firinistcinia have the movabl(> shoidder 

 girdhi which cliaracteri/es those of tiie arcilerous di\ isicui, the consoli- 

 dation constituting a niodiliciition superadded in attaining maturity. 

 Furthermore, young Salientia are toothless, :ind (uie section of the spe- 

 cies (»f Arcifera never ac(|iiire t«'elli. In these (the Ibitonida-) we have 

 a group which is imperfect in two points instead of one. 



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iicili-iniis I.\1M' {Si-iiiihidiiiiK li"lhi'ii''ki\. V\)l. h. Uniiit li'Oi, 

 . ilii , iiili.ll. Iiiiiiist<ini:il l.vpi . I'"ii;s. h iiiiil c 1111111 I'liiUi r. 



SliMiililir ,i;irilli-i nl' Aiiiir.i, I'i:;, a iilllii 

 liiiiiiriii, lailpuli' "illi liiiililini; liiiilih. I'ij;. 



As primitive I'latiachia aic toothed, it is evident that the toothless 

 condition of the Ibilonida' aiitl s(»m«' other fandlies is due to retar- 

 dation or degeneracy. The aiciterous st«'rnum is, on the other hand, a 

 primitive coiulilion, siiu'c it prevails in the Trodcla, and also in the 

 S|»'gocephali and Kachitond uf tln^ ('ai Iwuiifcroiis Age, in the latter 

 associated with mt'diau sternal t'lcnu'uts. The roofing in of the 

 Fustachian Inites seen in the Aglossa is also a character sup»'radded to 



tl 



le primitive coi 



idilion, as the loss of tongnt; is a case of subtraction. 



