578 



AN INTRODUCTION TO ENTOMOLOGY 



from 



The hooks or crotchets with which the prolegs of caterpillars are 

 armed vary in their arrangement in different families and thus afford 

 useful characters for the classification of these larvae. These hooks 

 are usually arranged in a circle or in rows on the tip of the proleg. 

 When they are in a single row or series, they are said to be uniserial; 

 when in two concentric row^s, biserial; when in several rows, multi- 

 serial. When the hooks of a row are uniform in length throughout 

 or shorter towards the ends of the row, they are said toheumordmal; 

 when they are of two alternating lengths, biordinal; when of several 

 lengths, multiordinal. The tip of a proleg on which the hooks or 

 crochets are borne is termed the planta. 



In most lepidopterous larvee the clothing of setse is comparatively 

 inconspicuous; such larvae are commonly termed naked in contra- 

 distinction to the 



^^^"^^31 --r^!;te:l7^. - hairy caterpil- 



^- -^ ' iaj-s_ But in the 



so-called naked 

 larvae, each seg- 

 ment of thebody, 

 when not too 

 highly special- 

 ized, is armed 

 with a definite 

 number of setae 

 which occupy 

 definite posi- 

 tions. Each seta is borne on a small chitinous tubercle; the number 

 of these setijerous tubercles and the positions they occupy differ in the 

 different families, and, therefore, afford characters which are much 

 used in the classification of Lepidoptera, 



The small tubercle bearing a single seta (Fig. 716, a) is evidently 

 the primitive form of setif erous tubercle ; for it is the only form f oimd 

 in the more generalized families. In some of the more specialized 

 families the tubercles are larger and many -haired (Fig. 716, b)\ this 

 type of tubercles is termed a verruca; it is characteristic of the so- 

 called hairy caterpillars, as, for example, the larvae of most of the 

 Arctiidae. In the larvae of the Satumioidea and of certain butterflies, 

 some of the tubercles are spinose projections of the body-wall (Fig. 

 716, c)\ such a projection is termed a scolus. 



Some caterpillars are clothed with more or less numerous setae 

 which are scattered and which have no constant position ; such setae 

 are termed secondary setce, in contradistinction to those borne on 

 setif erous tubercles which are of a definite number and occupy definite 

 positions; these are termed primary setce. Among the setif erous 

 tubercles that are constant in position, there are a few that are not 

 present in the first instar of generalized groups ; although the setae 

 borne by these tubercles are regarded as primary set£e when con- 

 trasted with secondary setae, they are distinguished from those found 

 in the first instar as subprimary setce. 



Fig. 716. — ^Types of setif erous tubercles. 

 Dyar.) 



