. Smithsonian miscellaneous collections. osternites. In some insects,however, in which there are laterosternal plates not united with thesterna (figs. 16 A, 17), the origins of the sternal apophyses (sa) arestill well within the sternal margins; and in an aeschnid nymph ( B) the apodemal invaginations (sa, sa) are removed from theapparent margins of the laterosternite sections (Ls) of the definitivesternum. From evidence of this nature the writer would regard thesternal apophyses as invaginations in the primary sternal plate itself(fig. 18 B, Stn), though there is much in favor of Webers
. Smithsonian miscellaneous collections. osternites. In some insects,however, in which there are laterosternal plates not united with thesterna (figs. 16 A, 17), the origins of the sternal apophyses (sa) arestill well within the sternal margins; and in an aeschnid nymph ( B) the apodemal invaginations (sa, sa) are removed from theapparent margins of the laterosternite sections (Ls) of the definitivesternum. From evidence of this nature the writer would regard thesternal apophyses as invaginations in the primary sternal plate itself(fig. 18 B, Stn), though there is much in favor of Webers view. Themesostemum of wingless females of the black aphis. Aphis fahae, NO. 2 THORACIC MECHANISM OF A GRASSHOPPER SNODGRASS 29 Weber (1928a) says, presents a case in which there can be no doubtthat the furca arises at a point between the basisternite, the furcaster-nite, and the subcoxal laterosternite. In the higher insects the sternal apophyses approach each other ineach segment and unite upon a common basis produced by a median Fig. Diagrams suggesting the theoretical evolution of a thoracic sternum. A, primitive condition in which the ventral sclerotization consists of alter-nating segmental sternites (Stn) and intersegmental intersternites (1st) ; theleg basis (LB) is an undivided coxopodite. B, primary sternite marked by the pits (sa) of a pair of internal apophyses,intersternite (1st) by the pit (spn) of a median process, or spina; leg basis(A, LB) subsegmented into subcoxa (Sex) and coxa (Cx), articulated dorsallyand ventrally (d). C, area of primary sternite (A, B, Stn) divided into basisternum (Bs) andsternellum (SI) by a fureal suture (k) forming an internal fureal ridge betweenbases of sternal apoph3rses; the following intersternite has become a spinaster-num (Ss) by union with segmental sternite; subcoxa (Sex) united ventrallywith sternum. D, typical definitive sternum, composed of primary sternite (A, B, Stn), a pairof subcoxal laterosternites (Ls, Ls), and the
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Keywords: ., bookauthorsm, bookcentury1800, bookdecade1860, booksubjectscience
