Article XXIV. — WORKER ANTS WITH VESTIGES OF WINGS. 



By William Morton Wheeler. 



Plate XIV. 



In 1878 Dewitz published an important contribution to our 

 knowledge of the postembryonic development of the appendages in 

 insects. 1 Among the forms which he studied were the worker larvae 

 and pupffi of a common European ant (Formica rufa). He investi- 

 gated their imaginal discs and discovered minute vestiges of wings 

 which could be traced into the pupa stage. Concerning these struc- 

 tures he says (p. 82): "The imaginal discs of the vestigial wings arise 

 later than those of the legs but nevertheless before the last larval 

 ecdysis. They are situated on the sides of the two posterior thoracic 

 segments, near their hind margins, and are drawn down close to the 

 ventral surface [PI. XIV, Fig. i b and c]. Hence they are much further 

 from the row of stigmata than from the leg-discs and lie just above the 

 broad muscle band that runs along each side of the ventral surface. 

 An elongate thickening with its two ends directed towards the ventral 

 and dorsal surfaces and having a long slit-shaped invagination, arises 

 in the hypodermis. The disc enlarges while the invagination pro- 

 gresses inward, so that two parts are differentiated, as in the develop- 

 ment of the legs: an enveloping membrane and lying within it a 

 more massive portion, the rudiment of the wing." 



The further development of these "wing-pockets corresponds 

 exactly with that of the leg-pockets. Each is an invagination of the 

 hypodermis towards the interior of the body and opens outward by 

 means of an orifice. In both cases growth is accompanied by an 

 enlargement of the enclosed appendage." 



During the pupal stage of the worker "the wings do not increase 

 in size, since they have reached the acme of their growth in the fully 

 developed larva." Traces of the wings are still visible in the semi- 

 pupa 2 but the little sacs finally flatten out and apparently become 

 portions of the general hypodermis in the older pupa. Dewitz shows, 

 nevertheless, a small vestige of the hind wing in a profile view of the 

 thorax of a completed worker pupa (PI. XIV, Fig. 2 b). 



' Beitrage zur postembryonalen Gliedmassenbildung bei den Insecten. Zeitschr f. wiss. Zool.. 

 XXX. Suppl., 1878, pp. 78-105. Taf. v. 



^ According to Dewitz the term semipupa was introduced by Packard (Observations on the 

 Development and Position of the Hymenoptera, with Notes on the Morphology of Insects. Proc. 

 Boston Soc. Nat. Hist., Vol. X, Boston, 1866; and the term pseudonymph was subsequently given 

 to the same stage by von Siebold (Beitrage zur Parthenogenesis der Arthropoden, Leipzig, iS-i, 

 p. 3s). Although von Siebold's term seems to be the more generally used, especially in Germary 

 Packard's term not only takes precedence but is simpler and more appropriate. 



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