419] COLORS OF TIGER BEETLES— SHELF ORD 25 



first to take on the form that the part is to have in the adult. The tip 

 of the mandible is the first to show the distinct pointed form toward 

 the head, tooth after tooth being differentiated from the somewhat larger 

 mass of tissue which makes up the mandibular outgrowth. The same is 

 true of the other mouth appendages, labrum etc., they become more 

 hairy in form and stand well separated from the old pupal skin. In tin- 

 case of the leg the tarsal claws are the first differentiated and this pro- 

 cess appears to move in a general way toward the body, segment by 

 segment, the femor being last to be differentiated and last to receive the 

 pigment. The position of the pigmentation in the tibia corresponds to 

 the point of attachment of the flexor of the tarsi. This is early developed 

 and thus the tarsi are the first to become movable; at this time the 

 flexor and extensor of the tibia are not well developed, their muscle 

 striatums appearing indistinct, but become much more distinct and 

 definite in form a little later and the tibia becomes movable about the 

 time of this development of its pigment. A similar development occurs 

 on the proximal portions of the trochanters which are the attachment of 

 the muscles. The wrinkled condition of the femora helps to give it 

 rigidity and the legs are well enough developed to allow of sufficient 

 movement to release the animal from the pupal skin. The legs are at 

 first somewhat extended and subject to a considerable amount of move- 

 ment, and while the body is flexed and extended and the pupal skin 

 ruptured in the midline of the thorax the mandibles are then worked 

 as well as the other mouth parts and the head removed by repeatedly 

 throwing it backward. The animal gradually wriggles out of its skin 

 and the wings and elytra soon expand; the wings expand to the full 

 length inside of about 20 minutes after the animal emerges, and remain 

 thus for several hours. If for any reason the expansion of the wings 

 or elytra is interferred with, they always remain in the exact condition 

 in which they were placed by the adverse conditions, and if the wings 

 are not^ folded in the normal fashion at the proper time, they will 

 always remain completely extended. Their early pigmentation, if it is 

 associated with hardening, is probably an advantage to this process of 

 withdrawal or folding. 



It seems altogether probable that the peculiar manner of develop- 

 ment of the pigment is associated with the development of the structures 

 which are necessary to ectosis and that they accordingly represent de- 

 velopmental adaptations. In the case of the tiger beetles which do not 

 have the appendages pigmented in the adult the euticula must harden 

 without being pigmented. 



The animals emerge with the elytra entirely unpigmented and dur- 

 ing the first 4 to 8 hours little change is easily noted. One can hardly 

 record the beginnings of the pigmentation as this is very faint, and the 



