196 SOME SINGULAR THINGS 



thoracic segment, indeed, is the subject of great 

 specialization and differentiation, and often differs 

 widely in its divisions, as also in the appendages 

 it bears, from the other thoracic segments ; but 

 this is not true, or is true in an extremely lim- 

 ited sense, as regards the other thoracic segments, 

 which to all practical purposes are identical in 

 general appearance with the abdominal and would 

 seem to have much the same office to fill. Yet, if 

 we examine carefully the dermal appendages of 

 these segments, we shall note some curious features 

 distinguishing them from those of the abdominal 

 segments. Thus, the spines, bristles, filaments, or 

 other special developments of the skin, are ranged 

 in most caterpillars of butterflies in longitudinal 

 rows when they have any regular disj^osition what- 

 ever. There may be one or two or more upon 

 each segment in a single row ; all the spines of one 

 row will be found at corresponding points of the 

 different segments, either on the middle or back or 

 front, as the case may be. Yet with scarcely an 

 exception among the caterpillars of butterflies, 

 those series which extend along the abdommal seg- 

 ments will either stop altogether at the thoracic 

 segments or slightly change their direction at this 

 point, so that often we may readily distinguish the 



