46 ILLINOIS BIOLOGICAL MONOGRAPHS [46 



specifically from the last pair, those of segment 10 are known as the anal 

 prolegs and the others as the ventral. 



The tip of the proleg on which the hooks or crochets are borne is 

 called the planta. In the most generalized forms (e. g. Pseudauaphora, 

 Hepialus) this planta bears a complete circle of well developed crochets 

 surrounded by several more circles of smaller ones. In Hepialus the 

 differences between the inner and outer are not as marked as in Pseudau- 

 aphora (Fig. 96). This arrangement is a multiserial circle and is con- 

 fined to Hepialidae, Acrolophidae, and Yponomeutidae. From it the 

 crochets may be lost in the mesal and lateral parts of the circle as in 

 Adela (Fig. 94), resulting in two transverse multiserial hands, which 

 degenerate in Incurvaria to a single transverse uniserial band. Where 

 the outer circles entirely disappear the resulting condition is known as 

 a uniserial circle (Fig. 101), for the crochets are in a single, continuous 

 series. 



The uniserial circle has the bases of all the crochets in line but the 

 lengths are seldom uniform. We are able to distinguish uniordinal cro- 

 chets (Fig. 105), in which the tips as well as the bases are in a straight 

 line, from the hiordinal (Fig. 106), in which the crochets are of two 

 distinct lengths alternating. Occasionally triordinal crochets (Fig. 98) 

 are seen, but Forbes 's separation of Rhopalocera from Heterocera on 

 this basis fails tc be confirmed by observation. In fact the irregularities 

 in the lengths of the biordinal crochets make any extensive use of the 

 difference in the number of sizes inadvisable. On the other hand the 

 uniordinal series is usually definite, and the irregularities, except at the 

 ends of the row, are negligible. 



Having a complete uniserial circle of crochets, a group may develop 

 transverse bands (Fig. 99) by the loss of both the mesal and lateral 

 parts of the circle, or a penelUpse (L. paene-\-ellipsis, "almost an el- 

 lipse") by the loss of only a short portion on one side. The penellipse 

 may be lateral as in Psychidae (Fig. 85), where the gap in the series is 

 near the meson; or it may be mesal as in Pyraustinae (Fig. 98), where 

 the lost crochets were farthest from the meson. 



Finally more than half the circle may be lost and a mesoseries 

 (Fig. 105) result. This is the arrangement seen in nearly all the Macro- 

 lepidoptera except Hesperoidea. In certain families a few rudimentary 

 hooks remain (or are secondarily developed) on the lateral portion of 

 the planta. As there is no case in which these even approach the size 

 of the mesal crochets there is no likelihood of this condition, to which 

 the term pseudocircle (Fig. 97) may be applied, being confused with a 

 circle or penellipse. 



The crochets of a mesoseries, penellipse, or circle may be either uni- 



