PRESENT KNOWLEDGE OF THE PROTURA. 227 



detail the chief structural points on which their systematic 

 position will depend. 



The antennae are completely absent in all known forms, 

 Schepotieff's account of the antennae of Protapteron indicum 

 [16] having been shown by Rimsky-Korsakow [13] to have been 

 an error.* 



The mouth parts are entotrophic and somewhat resemble 

 those of the Collembola. There are a pair of simple style- 

 like mandibles and two pairs of maxillae (or maxillae and 

 labrum), each consisting of an inner and an outer lobe and 

 a jointed palp. The maxillary palp is much larger than the labial 

 palp and projects beyond the head at each side of the mouth. 



The number of abdominal segments in the adult is twelve, a 

 number which is not found in any insect except in the 

 embryonic stage. The earliest known larval stage, however, 

 has only nine segments, the remaining three being interpolated, 

 one at a time, between the ultimate and penultimate segments. 

 This increase in the number of segments during life, or 

 anamorphosis, is a Myriapod character, though in these the 

 segments appear in groups (e. g. in Jalus terrestris, five at a 

 time). 



The abdominal appendages are situated in pairs on the 

 first, second, and third abdominal segments. In the family 

 Eosentomidae (see later for classification) all are two-jointed, the 

 second joint being small, retractile into the first, and with a 

 small protrusible vesicle at the tip; in the Acerentomidae, how- 

 ever, only the first pair are two-jointed, the others consisting of 

 a single joint and all being much smaller than in the previous 

 family. 



Anal cerci are completely lacking, and the ter- 

 minal segment is truncate and shaped not unlike 

 the telson of a crustacean, to which character 

 they owe their name "Prot-ura," "primitive tail." 



The genital system in the female consists of 

 two ventral paired ovaries and oviducts, each side 

 forming a large straight unbranched tube reach- 

 ing from about the metathorax to the ninth seg- 

 ment, where they unite into a short vagina and 

 open by a single pore between the eleventh and 

 twelth segments. In the male there are two large 

 testes which unite in front at about the level of the 

 mesothorax, and long curled vasa deferentia open- ,fte- a.-Diagrama 



. . y • i • i i °' terminal segments 



ing separately on the penis, which can be pro- of male (beiow) and 

 truded between the eleventh and twelth segments. femaIe (above) ' 



* Rimsky-Korsakow also states that Schepotieff was mistaken in bis 

 accounts of the mouth parts, abdominal appendages, and genital opening, 

 and that his species Protapteron indicum is a quite typical member of the 

 genus Eosentomon. 



s2 



