64 OTHER 'MYRIAPODS' 



is covered with minute pustulations. On the twelfth day the outer 

 membrane breaks and the embryo partially emerges: its anterior 

 end becomes free while the posterior end is still enclosed in the 

 membrane. The embryo is covered by one embryonic membrane 

 which bears outgrowths that cover the antennae and three pairs 

 of legs are visible inside. The embryo remains motionless in this 

 condition for three days and then, by dorsal splitting of the second 

 cuticle, issues out as an actively moving hexapod larva with two 

 tactile setae (Harrison, 1914). The remaining instars have 5, 6, 8 

 and 9 legs respectively and the number of tactile bristles are 3, 4, 4 

 and 5. Before moulting the animals become somewhat rigid but 

 remain upright throughout the process. The head and antennae 

 are bent ventrally and when the process, which takes only about 

 twenty-five minutes, is almost complete, vigorous propulsions, 

 which first free the head, enable the white, moist and weak animal 

 to drag itself from its old cuticle. 



Class SYMPHYLA 



The reproductive organs of the Symphyla, like those of the 

 Pauropoda, open upon the third somite behind the head, but 

 otherwise the two classes are very dissimilar. In the Symphyla the 

 antennae are very long and many jointed, there are four pairs of 

 peculiarly modified jaws and the head bears a pair of tracheal 

 spiracles. There are twelve pairs of walking legs, but the number 

 of tergal plates, namely fifteen, the first being very small, is greater 

 than the number of legs and not less as in the Diplopoda and 

 Pauropoda. The basal segments of the legs of the third to twelfth 

 leg-bearing segments are provided with a protrusible sac thought 

 to have a respiratory function, whereas in Pauropods there is but 

 a single pair on the floor of the collum or first post-cephalic seg- 

 ment. With the last somite articulates a pair of tail-like processes 

 upon which spinning glands open, and just in front of them is a 

 papilla carrying a tactile hair. Symphyla are small, pallid arthro- 

 pods resembling tiny centipedes in appearance and activity, that 

 live in damp places under stones, dead leaves, etc. Two families 

 are known, Scutigerellidae and Scolopendrellidae, both of which 

 are represented in the British fauna. 



The class Symphyla has held the interest of many naturalists 



