232 



INVERTEBRATE ZOOLOGY 



the nephridia are also metameric in their arrangement. The 

 head bears three pairs of appendages. At the anterior extremity, 

 it bears a pair of ringed antennae and behind these a pair of 

 oral papillae. Two pairs of hooked plates within the mouth 

 cavity have been regarded as mandibles. Spiracles in longitu- 

 dinal rows, or scattered, communicate internally with respiratory 

 tubes which are in the form of tracheae. The genital ducts, 

 which are modified nephridia, opens just anterior to the anus. 

 The Onycophora are viviparous. In habits, they are nocturnal, 

 living during the day under bark and in decaying wood. 



Class 6. Myrientomata 



The minute arthropods included within the single order 

 Protura are recognized by some as comprising an independent 

 class to which the name Myrientomata has been applied. The 

 representatives of this class are somewhat 

 similar to the Thysanura in body form, but 

 antennae and cerci are both lacking. The 

 thorax bears three pairs of legs and on the 

 abdomen there are the vestiges of three pairs 

 of appendages. 



Most of the described species live in 

 humus. The group has been so recently 

 established and the species have been so 

 little studied that relationships to other 

 arthropods have not been well established. 



THE MYRIAPODS 



In the older literature, a number of 

 tracheate arthropods with numerous legs 

 Pauropus were considered as a single class under the 

 name Myriapoda. These forms present so 

 many differences in structure that at least 

 four distinct classes are now recognized under the names 

 Diplopoda (Class 7), Chilopoda (Class 8), Symphyla (Class 9), 

 and Pauropoda (Class 10). 



The Chilopoda show many evidences of close relationship 

 with the insects, while members of the genus Scolopendrella, 

 which represent the Symphyla, show remarkable combinations 

 of diplopodan and insectan characters. Except for the eleven 

 or twelve pairs of legs, Scolopendrella very closely resembles the 



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 huxlcyi. {After 

 yon) . 



Ken- 



