PRESENT KNOWLEDGE OF THE PROTURA. 229 



the mesothorax to a long cylindrical mesenteron. About the 

 region of the sixth abdominal segment this contracts again 

 to the narrow hind intestine, and at the junction there are 

 six very short Malpighian tubes, arranged in two groups of 

 three. 



The muscular system, which is not of much interest in the 

 present discussion, has been fully worked out by Berlese [5] and 

 Prell [12] , while other points of interest are the paired glands 

 which open on the eighth abdominal segment, and the presence 

 of a single claw on the tarsus which is a Collembolon and 

 Myriapod feature. 



The various views which have been put forward as to the 

 systematic position of the Protura depend chiefly on the relative 

 importance which the writers assign to the various structural 

 characters we have considered, the whole question being the 

 more difficult as, in the absence of any knowledge of their 

 embryology, it is often impossible to decide whether any par- 

 ticular feature is primitive or the result of specialization. 



Silvestri [18] first described them as an order Protura of the 

 subclass Apterygota of the Insecta. Berlese [5] , considering the 

 lack of antennae, the anamorphosis, and the large number 

 of segments, removed them from the Insecta and treated them 

 as an order Myrientomata of the class Myriapoda. 



Schepotieff [16] united them with Campodea as a suborder 

 Prothysanura of the Thysanura. 



Borner [8] , considering the entotrophic mouth-parts, and 

 the lack of anal cerci to be more important than the lack of 

 antennas, which he believes to be secondary, makes them an 

 order of the Apterygota, and proposes the following classifica- 

 tion for that subclass : — 

 Subclass Apterygota. 



Super Section Ectotropa. 



Order 1. Archeognatha ... Machilidae. 



Order 2. Thysanura Lepesmatidae and Nicoletidas. 



Super Section Entotropha. 

 Section a. Archinsecta. 



Order 3. Diplura Campodeidae, Japygidae, and 



Anagapygidas. 

 Section b. Ellipura. 



Order 4. Protura (Protapteridee) Eosentomidae, 



Acerentomidae. 



Order 5. Collembola Poduridae, Entomobryidae, Ne- 



elidae, Sminthuridas. 

 At this time the supposed possession of antennas by Pro- 

 tapteron had not been contradicted, and their presence in a 

 Proturon would have given more justification to the close 

 relation which Borner supposes between these insects and the 

 Collembola. 



Rimsky-Korsakow [13] considers the absence of antennae may 



