250 KINGSLE V. [Vol. V 1 1 1 . • 



structures are absent from the Chilopods (as from the Hexa- 

 pods), except in a few Geophilidae, where repugnatorial glands 

 occur, opening by foramina in the mid-ventral line. 



In the Chilopods the reproductive organs consist of paired ^ 

 gonads situated above the alimentary canal and opening to the 

 exterior by ducts which are at first paired, but which later 

 unite into a common tube which leads to a single external 

 opening situated in the penultimate segment of the body. In 

 the Hexapods the conditions are almost exactly the same ; the 

 gonads are dorsal, the genital ducts unite (except in Ephem- 

 eridae), and there is a single external opening, always at the 

 posterior end of the abdomen. In both Hexapods and Chilo- 

 pods the spermatozoa are motile. In the Diplopods there is 

 a single unpaired gonad situated beneath the alimentary canal, 

 and the genital duct, passing forward, divides into two, each 

 of which has its own opening at the bases of the legs of the 

 second post cephalic segment. The spermatozoa are quiescent. 



We know so little of the embryology of the Myriapods that 

 the aid of development can be had to only a slight extent in 

 our comparisons, but the facts which it affords seem important. 

 In the Chilopods the embryo escapes from the egg with nu- 

 merous ambulatory appendages, a pair to each somite. The 

 same is true of the typical Hexapods, all later observers agree- 

 ing that a polypod precedes a hexapod condition. The young 

 Diplopod escapes from the egg in a hexapod condition, and 

 the presence of these six legs has been seized upon as a proof 

 of the near association of these forms. An exact comparison, 

 however, seems to show that the two are in reality very unlike 

 as appears in the following table.^ 



1 Single in Scolopendra. 



2 As nothing is known of the existence of a tritocerebral segment in the Diplo- 

 pods, the comparison can only be made upon the basis of the appendages of the 

 adult. If the tritocerebral segment should prove lacking in the millepeds the 

 contrast will prove stronger than it now is. The statement of the Diplopod 

 appendages is based upon Heathcote ('88). 



