TITANOSOMA AND POLYMICRODON IN ENGLAND 



155 



sufficient to explain the rare and sporadic occurrence of these 

 remarkable millipedes. 



The Larval Stages of Titanosoma. 



It is owing to the care with which Mr. Bagnall collected 

 these Diplopods in the field that I have been able to bring 

 together a complete developmental series. I give in the first 

 place the following summary : — 



1st larva with 3 pairs of legs, 7 abdominal segments, 1 5 antennal joints. 

 2nd ,, 6 ,, 10 ,, 7 ,, 



3rd ,, II 





12 „ 7 „ 



4th „ 17 





15 » 7 



5th „ 21 





17 „ 8 



6th ,, 23 





)i *8 ,, 8 ,, 



7th. Adult 29 





19 „ 8 



The appendages 



of the first larva are as follows : — 



Collum-segment ... ... ... pair of legs. 



2nd abdominal segment ... ... 1 ,, 



3rd 



,, 



1 



4th 



j) 



1 



5* 



•3 







6th 





,, ,, 



Pre-anal 



and 



anal segment... ... ,, 



The number of appendages of the abdomen agrees there- 

 fore in the first larval stage with those of Polydesmus. On the 

 contrary, in many of the first larvae of other Diplopods only a 

 single segment without limbs occurs between the telson and 

 the third limb-bearing segment : this is the case for example 

 in the Thaumaporaiia larvae which I investigated last year. 



The first larvae of Titanosoma are distinguished from all the 

 others by the characters of their bristles ; for whilst the second 

 to sixth larvae show, like the adults, exceedingly short bristles 

 on the pleurotergites, the first larva possesses much longer 

 bristles. Their arrangement in three rows is the same as in 

 subsequent stages, but the individual bristles are not only 

 two to three times longer than in these stages, but are also 



1 The telson is reckoned as a single segment. 



