BY VERA A. IRWIN-SMITH. 



803 



setae, were compound. The distal segment is much smaller than 

 in the case of the ventral setae, and can be seen only with the aid 

 of an oil immersion lens. The setae are hollow, and slightly 

 swollen at the base. They are bent forward, arching over the 

 rostrum, but do not reach quite to the anterior margin. 



The trunk-hairs (Fig. 4 9, t.h.) are short and slender, not more 

 than 0'012 nnn. long, and are not swollen at the base. They 

 are arranged in eight longitudinal rows, the two rows on each 

 surface, dorsal, ventral, and lateral, being situated close together. 

 Each hair is inserted in a pit-like depression in the cuticle, from 

 the base of which, a fine canal runs inward to the inner body-wall 

 (Fig.51, t.h.). The rows extend over the rostrum to the serrated 



margin of the cuticle, where 

 the terminal hairs form a 

 circle surrounding the pro- 

 minence on which the mouth 

 is situated (rig.48). The hairs ^'^^^ 

 become longer towards the 

 anterior end (0*022 mm.), and 

 are especially long on the 

 rostrum, where there are three 

 strong hairs in each row. 

 Those on the ventral side of 

 the rostrum are nearly as stout 

 as the dorsal setae, so that, 

 under low magnification, they 

 give the appearance of a cir- 

 cular fringe of stout hairs sur- 

 rounding the anterior end. 



TW.d. 



mb 

 S.c 



m.b. 



Fiy.31 



Fig. 51. — X. tenax. 



Transverse section through anterior 



region of trunk; ( x 950). 



The ventral rows of trunk hairs are 

 continuous with the rows of ventral setae. The lateral grooves 

 (Fig. 48, l.o.) lie between the two lateral rows of hairs on each 

 side of the rostrum. They are large, and horseshoe-shaped or 

 hook-shaped, with the open end directed posteriorly. 



On account of the toughness of the cuticle, satisfactory longi- 

 tudinal sections are difficult to obtain, but some transverse sections 

 show the internal structure fairly well. The thick cuticle (Fig.51, 



