. Smithsonian miscellaneous collections. surfaceand reduce the primary sclerotization to two or more widely separatedplates. Or again, an original sclerotic area may be contracted to arelatively small sclerite, or it may be obliterated. It then becomes aquestion, if the primary plate has been given a name, whether we areto apply this name to the area originally occupied by the plate, orrestrict it to the sclerotic remnants or remnant. It is the usual prac-tice to apply the name only to the sclerite, whatever its extent, and,if the sclerite is obliterated, to say that the part in question is ob
. Smithsonian miscellaneous collections. surfaceand reduce the primary sclerotization to two or more widely separatedplates. Or again, an original sclerotic area may be contracted to arelatively small sclerite, or it may be obliterated. It then becomes aquestion, if the primary plate has been given a name, whether we areto apply this name to the area originally occupied by the plate, orrestrict it to the sclerotic remnants or remnant. It is the usual prac-tice to apply the name only to the sclerite, whatever its extent, and,if the sclerite is obliterated, to say that the part in question is obsolete NO. 2 THORACIC MECHANISM OF A GRASSHOPPER SNODGRASS 3 or lost. This usage has convenience for descriptive purposes, but it islikely to confuse our morphological conceptions, since an anatomicalpart is the same thing regardless of the nature of its surface covering. I. GENERAL DISCUSSION If all that has been written about the thorax of insects were true,or could be made to fit with our present knowledge of insect struc- Pc acs Sex. Eutn Fig. I.—Diagram of the theoretical structure of a primitive thoracic segment. The tergum (T) includes the segmental and preceding intersegmental sclero-tization of the dorsum; the ventral sclerotization consists of a primary seg-mental sternal plate (Stn) and intersegmental intersternites (Ist) ; the pleuralarea is occupied by a basal subsegment of the leg, the subcoxa (Sex), divideddorsally into a eupleuron (Eiipl) and a eutrochantin {Eutn). acs, antecostal suture; c, d, dorsal and ventral subcoxo-coxal articulations;Eupl, eupleuron; Eutn, eutrochantin; Isg, primary intersegmental line; 1st, in-tersternite; Mb, secondary intersegmental membrane; Pc, precosta; Sex, sub-coxa; Stn, primary sternite; T, tergum. ture, there would be little need of prefacing a special description ofthe thoracic skeleton and musculature of the grasshopper with a gen-eral discussion. Science, however, is not a collection of facts but aconcept in which to hold t
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