THE PROBLEMS OF TRANSFORMATION 257 



some facts in the life-histories of certain Coleoptera suggest 

 a simpler and more natural sequence of events. The larva 

 of Tenebrio molitor, familiar as the " mealworm ", has been 

 observed occasionally 1 to bear pairs of outward wing- 

 -rudiments on the second and third thoracic segments (Fig. 

 123 a). Also in the life-history of a small ground-beetle 

 (Lebia scapularis) it has been recently shown that 2 a " pro- 

 nymph ' ' stage with short external wing-rudiments (Fig. 

 123 b) precedes the pupal stage (c). A similar pre-pupal instar 

 with external wing-rudiments occurs also in some males 



FIG. 123. 



, " Mealworm " (larva of beetle, Tenebrio molitor) with abnormal external 

 wing-rudiments (side view). x 2. After Heymons, Ergeb. u Fortschr. Zool. I. 

 b, final larva, and c, pupa of ground beetle, Lebia scapularis (dorsal view) 

 (b, with its small external wing-rudiments is a " pre-pupa "). x 8 After 

 Silvestri, Redia II. 



of [the remarkable parasitic Strepsiptera (p. 118). Such 

 a precocious appearance of wing-rudiments is most unusual 

 among the Endopterygota generally, and in the case of 

 Tenebrio it is abnormal for the species, but it is highly 

 instructive to students of the course of insect trans- 

 formations, because, if we accept these abnormalities as 

 examples of reversion to an old, ancestral condition, we 

 conclude that among the ancestors of the primitive endoptery- 

 gote insects wing-rudiments appeared outwardly before the 



1 R. Heymons : " Fliigelbildung bei der Larve von Tenebrio molitor ". 

 Sitzb. d. Gesellsch. naturforsch. Freunde, Berlin, 1896. 



2 F. Silvestri : " Metamorfosi e Costumi della Lebia scapularis ". Redia 

 II. 1905. 



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