142 BRISTLE-TAILS AND SPRING-TAILS. 



form of the Myriopodous head, the front, or clypeal region 

 being reduced to a minimum, and th,e antennae and eyes brought 

 in closer proximity to the mouth than in any other insects." 



Sir John Lubbock has given us an admirable account of the 

 internal anatomy of these little creatures, his elaborate and 

 patient dissections filling a great gap in our knowledge of their 

 internal structure. The space at our disposal only permits us 

 to speak briefly of the respiratory system. Lnbbock found a 

 simple system of trachea? in Smynthurus which opens by "two 

 spiracles in the head, opposite the insertion of the antenna^" i. 

 e., on the back of the head. (Von Olfers says that they open on 

 the prothorax.) Nicolet and Olfers claim to have found tracheae 

 in several lower genera (Orchesella, Tomocerus, and Achorutes 

 and allied genera), but Lubbock was unable to detect them, and 

 I may add that I have not yet been able after careful search to 

 find them either in living specimens, or those rendered trans- 

 parent by potash. 



Having given a hasty sketch of the external aspect of the 

 Poduras, I extract from Lubbock's work a synopsis of the fam- 

 ilies and genera for the convenience of the student, adding the 

 names of known American species, or indications of unde- 

 scribed native forms. 



SMYNTHURID^K. Body globular or ovoid ; thorax and abdomen 

 forming one mass ; head vertical or inclined ; antennas of four 

 or eight segments. Eyes eight on each side, on the top of the 

 head. Legs long and slender. Saltatory appendage with a 

 supplementary segment. 



Smynthurus. Antennas four-jointed, bent at the insertion 

 of the fourth, which is nearly as long as the other three, and 

 appears to consist of many small segments. No conspicuous 

 dorsal tubercles. (In this country Fitch has described five spe- 

 cies : S. arvalis, elegans, hortensis, Novaeboracensis, and signi- 

 fer. Figure 156 represents a species found in Maine.) 



Dicyrtoma. Antennae eight-jointed, five before, three after 

 the bend. Two dorsal tubercles on the abdomen. 



Papirius.* Antennae four-jointed, without a well-marked 



* Lnbbock considers that Papirius should be placed in a distinct family from 

 Smyuthurus, because it wants tracheae. Their presence or absence scarcely seems 

 to us to be a family character, as thpy are wanting in the Poduridae, and are not 

 essential to the life of these animals, while in other respects Papirius seems to 

 differ but slightly from Smynthurus. 



