212 Life History of Wireivorms 



number only about seven to eight in the thoracic and five to six in the 

 abdominal spiracles. 



Towards the anterior end of the atrium there is attached an apparent 

 strut, connecting the atrium with the outer cuticle near the anterior end 

 of the spiracle but a little more dorsal and running at right angles to the 

 axis of the spiracle. This "strut" is moulted with the exuvia. It is not 

 present in the first larval instar, although present in the second and 

 subsequent ones. Evidently it is the scar left by the withdrawal of 

 the trachea at the last preceding ecdysis, as was pointed out by 

 Schiodte(i2, at p. 493). At the point where the trachea has been with- 

 drawn through the cuticle there is an oval scar of a brownish colour at 

 the margin and sometimes bearing a septum of similar colour through 

 its long axis. The central area of this scar is covered with yellow chitin, 

 similar to the general colour of the cuticle and was evidently deposited 

 subsequently to the withdrawal of the trachea. 



At ecdysis the position of the spiracle is moved back a Httle and the 

 lining of the atrium, with a considerable length of tracheal lining from 

 beyond it, comes away with the exuvia, leaving the scar in the body of 

 the newly moulted larva anterior to the new spiracle. This moving back 

 of the spiracle at each ecdysis does not however imply any change in 

 its position in each instar relative to the other parts of the body, as 

 measurements have shown. The extent of the change of position therefore 

 merely corresponds to the increase in growth of the larva. 



The necessity for some provision to avoid the difficulty of extracting 

 whole a tracheal tube through a biforous stigmatic opening is manifest. 

 This phenomenon of the growth of a completely new spiracle, alongside 

 the old, appears to resolve the difficulty. 



De MeijerelO) found somewhat similar remnants of spiracles in the 

 case of amphipneustic dipterous larvae, although in the cases dealt with 

 by him the cause was apparently the covering of the stigmatic orifice by 

 a membrane, usually complicated, which could scarcely be renewed after 

 ecdysis had taken place. 



Boving(3) deals with the anatomy and functions of biforous spiracles 

 in coleopterous larvae and speaks of a "spiracular slit" near the spiracle 

 in Hister, which he figures, as well as sections of the spiracles of a larval 

 Elaterid from Java. In neither of these cases do his sections show the 

 "spiracular slit" completely closed, but probably in both cases it repre- 

 sents the scar of the trachea just described. 



Scott (13) found biforous spiracles of very similar structure in the 

 larva of Epuraea depressa, but he does not describe any scar. 



Not infrequently larvae are found having one or more "bHnd" 



