ENTOGNATHY IN APTERYGOTES — TUXEN 381 



couvrement par un 'pli oral' des genas et postgenas, reunissant 

 clypeus et labium et s'etendant, comme un volet, au-dessus des mandi- 

 bules et maxilles. . . . Le pli oral derive d'anciens epipodites 

 subcoxaux." 



Snodgrass (1952, p. 271) writes: "The mandibles and maxillae 

 are enclosed in pockets of the head formed by a union of the labium 

 M^ith the lateral walls of the cranium." In 1951 (p. 81) he refers this 

 concept to the classical embryological investigation by Folsom (1900), 



Paclt (1956b, pp. 17-18) writes: "Bei den Collembolen und Pro- 

 turen beschrankt sich die Mundoffnung auf den rein frontalen Teil 

 des Kopfes, weshalb die hier tiefer versenkten Mundgliedmassen 

 dauernd in der Mundhohle versteckt bleiben und von den Seiten 

 nicht sichtbar sind. Gerade entgegengesetzte Verhaltnisse beobachtet 

 man bei den Dipluren, wo die frontolaterale Lage der Mundoffnung 

 es dem Tier ermoglicht, die Mundgliedmassen teilweise nach aussen 

 hin auszusetzen. Da aber auch die Mundteile der Dipluren in die 

 betrefifende Einstiilpung des Kopfes tief versenkt sind, werden die 

 Collembolen, Proturen und Dipluren gemeinsam als Entognatha . . . 

 bezeichnet." 



In an attempt to form a personal opinion in this matter I have 

 investigated many specimens of one species of each of the three 

 groups, namely Acerentomon doderoi Silv. (from Birkezwischenmoor 

 am Hoftsee, Holstein, February 1941, Strenzke leg.), Onychiurus 

 armatus TuUb. (from Berufjordur, Iceland, in great numbers on the 

 shore, July 14, 1900, A. C. Johansen leg.), and Campodea plusiochaeta 

 Silv. (from Hellebaek, Denmark, 1893, C. With leg.). Of course an 

 investigation of a greater number of species would have been de- 

 sirable, but time did not permit this. In the present paper the follow- 

 ing elements will be treated comparatively in the three groups : The 

 antennae, the entognathy, the hypopharynx and fulcrum, the mandi- 

 bles, and the maxillae. 



1. THE ANTENNAE 



Imms in 1940 made a fine study of the antennal muscles in different 

 groups of arthropods and arrived at the very important conclusion 

 that the arthropod antennae were divisible into two groups, segmented 

 antennae and annulated antennae, the first group having intrinsic 

 muscles in all segments, the second possessing intrinsic muscles only 

 in the pedicel, consisting of from one to four segments, the rest of 

 the antenna lacking independent movement. Segmented antennae 

 were found in all groups known as Myriapoda (though a transitional 



