384 SYNOPTIC COLLECTION. 



The preparation of Julus (No. 942, specimen on the 

 left), gives the ventral view and exhibits the segments 

 separated from one another. Most of these segments 

 have two ventral plates instead of one apparent plate as in 

 the dorsal view. These ventral plates are extremely small 

 and so narrow that the legs which are fastened to them 

 are crowded closely together. 



It is seen that the three complete anterior segments 

 (which are probably thoracic) carry one pair of legs, while 

 the remaining segments which are abdominal, excepting 

 the first (the appendages of which are modified for repro- 

 ductive purposes), and last, carry two pairs of these 

 appendages. 



The light thrown on the structure of Myriapods by 

 Palaeocampa and Archipolypoda enables one to see that 

 each apparent abdominal segment of the Diplopoda 

 is most probably made of two segments, the dorsal plates 

 of which have become fused. Furthermore, the two ventral 

 plates of each thoracic segment have likewise fused into 

 one plate, and at the same time one pair of legs has dis- 

 appeared. The present condition of these segments is 

 therefore not primitive but rather secondary and special- 

 ized. 



The head of Julus is free, as we have said, but is so 

 bent down as to be concealed under the body in a dorsal 

 view. It bears a cluster of ocelli on each side, one pair 

 of jointed antennae, a labrum or upper lip, a pair of 

 mandibles, and one pair of maxillae. In the preparation 

 the sternal plate of one of the cephalic segments is seen. 



The Julidae breathe by means of tracheae which do not 

 arise until the animal is hatched (Packard). The openings 

 of spiracles occur on each of the ventral plates. The 

 tracheae are in the form of tufts of tubes which never join. 



The Diplopoda leave the egg in a very immature con- 

 dition when only three pairs of legs are formed. These 

 are small, partially developed, and are not fastened to 

 consecutive segments, one segment being skipped. 



