802 



ON THE CH^TOSOMATID^, 



ir o 



side of the anus. The number varies, in the specimens examined, 

 from seven compound and five simple, to fifteen compound and 

 seven simple set^e. In the inner rows, the setie are all compound, 

 and vary in number from 10-17. 



In the female (PL xlix.), all the setfe, of both outer and inner 

 rows, are compound, and vary in number, from nine in the outer 

 and ten in the inner, to twenty in the outer and twenty-two in 

 the inner rows. All the compound seta? in this species are com- 

 paratively short and stout. The proximal segment is hollow; 



while the distal segment is very 

 broad, with two, curious, lateral pro- 

 cesses, which are very characteristic 

 (Fig. 49a). In some of the younger 

 specimens, two, distinct, inner rows 

 of set{« are not fully developed. The 

 head-seta3 are not inserted on the 

 rostrum, but immediately behind it, 

 on the margin of the striated area 

 (Fig. 48, d.s.). They are ari-anged in 

 a semicircle on the dorsal side of the 

 head; and, in most adult worms ex- 

 amined, are eight in number, forming 

 two rows of four each. But, in one 

 female specimen, there is a third row 

 of two behind the other rows, the two 

 being inserted in a line with the 

 middle two of the rows in front. 



or. 



Ficr.oO 



tenax. 



L.S.throiigh cuticle, and bases {Several young specimens have only 



of ventral setas; ( x 830). r. » , . , i n , . 



one row oi tour seta?, with a fine hair 



inserted close to the outer mai-gin of each. In one case, a second 

 row appears to be just in process of foi'mation, in front of that 

 which is fully developed. In specimens deeply stained with 

 hiematoxylin, a small, jointed, distal segment is clearly discerni- 

 ble on each seta, the only case in which I have been able to dis- 

 tinguish this; though, in the other species examined, I have 

 thought it probable that the head-setae, as well as the ventral 



