The Origin of the Markings of Caterpillars. 175 



and most obvious designations, all of which have 

 already been employed by various authors, but not 

 in any rigorously defined sense. I understand 

 by the " dorsal line " that which runs down the 

 middle of the back ; the lines above and below the 

 spiracles will be respectively distinguished as the 

 " supra- " and " infra-spiracular " lines, and the 

 line between the dorsal and spiracular as the " sub- 

 dorsal line." The distinction between " ring- 

 spots " and " eye-spots " will be made manifest in 

 the course of the investigation. A glance at any 

 of the existing descriptions of larvae will show how 

 necessary it was to introduce a precise terminology. 

 Even when the latter is exact as far as it goes, 

 the want of precise expressions not only makes 

 the descriptions unnecessarily long, but it also 

 considerably increases the difficulty of comparing 

 one species with another, since we can never be 

 sure whether the same designation applies to the 

 same homologous character. For instance, when 

 the larva of Chcerocampa Elpenor is said to have 

 " a light longitudinal line on the sides of the 

 thoracic segments," this statement is indeed correct; 

 but it is not apparent whether the line is above or 

 below, and consequently it does not appear 

 whether it is the equivalent of the longitudinal 

 line " on the sides " of the segments in other 

 species. If, however, it is said that this line is 

 " subdorsal on the thoracic segments, and on the 

 eleventh abdominal segment," it is thereby indicated 





