54 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8 1 



and later by von Stumnier-Traunfels (1891). The latter writer called 

 it the " Stiitzegerust,'' or supporting framework of the hypopharynx ; 

 he figured it in Tetrodoiitopliura gigas and in Campodca staphylinus, 

 and he says it has essentially the same structure in Japyx, Campodea, 

 and Collembola. Folsom (1899) described the hypopharyngeal skele- 

 ton of the collembolan, Orchcsella cincta, as consisting of a thin 

 median plate with paired anterior, dorsal, and posterior arms. The 

 anterior arms, he says, are united with the lateral lobes of the hypo- 

 pharynx, the others are attached to the cranial walls by fibrous strands. 

 This structure of the collembolan head, upon which arise muscles 

 of the pharynx, the mandibles, and the maxillae, Folsom points out 

 is the true tentorium, homologous with that of the Orthoptera and 

 other mandibulate insects. The failure to recognize this fact, he 

 says, " has led students to assign an altogether undue importance to 

 the * Stutzapparat ' of the ligula (hypopharynx), which has errone- 

 ously been regarded as a sort of substitute for a tentorium." " Partly 

 as a result of this error," he adds, " systematists have acquired an 

 exaggerated opinion of the dififerences which separate Collembola 

 and Thysanura from insects of other orders." 



The tentorium of the Protura has been described by Berlese (1910) 

 and by Prell (1913). The anterior arms of the structure are united 

 in a median bar, but each arm itself is forked anteriorly, and the 

 two forks are said by Prell to make connections with the base of the 

 hypopharynx and with the fronto-clypeal ridge of the head. Both 

 Berlese and Prell call this endoskeletal structure of the proturan head 

 the " tentorium," but Prell observes that it has a close resemblance 

 to the " Zungenapparat " of the Collembola and suggests a homology 

 with this structure. It is now to be seen that the two structures are, 

 indeed, identical, and that the hypopharyngeal apophyses of the 

 Apterygota are the primary elements of the pterygote tentorium. 



In Machilis (figs. 21 E, 27 D), the hypopharyngeal apodemes 

 (HA) arise from suspensorial plates (fig. 21 E, HS) connected later- 

 ally with the cranial walls as in the chilopods, but their points of origin 

 from these plates are at the basal angles of the clypeus (Clp). There 

 is in Machilis also a well-developed posterior tentorial bar (PT) ex- 

 tending transversely through the back of the head from pits (pt) 

 in the lower ends of the postoccipital suture. The maxillary cardines 

 (Cd) are attached to the margin of the cranium just anterior to these 

 posterior tentorial depressions. The inner ends of the hypopharyn- 

 geal apodemes (HA), or anterior tentorial arms, of Machilis become 

 weak and fibrous, and in specimens cleaned in caustic they do not 

 connect with the posterior tentorial bar. The tentorium of Machilis. 



