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PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 47. 



usually curved more than in the female, and in Thysanotella, if 

 Bassett-Smith's figure be correct, it describes three-quarters of a 

 circle. These maxillipeds in the female have lost their function of 

 attachment organs, and are used only for pulling the head down to 

 the skin of the host and holding it while the parasite gets its food. 

 In Traclieliastes even this function is lost, and it is difficult to under- 

 stand how they can be used at all, situated as they are between the 

 bases of the second maxillae (see plate 40, fig. 106). 



The muscular system. — This is extremely simphfied, and is as 



much reduced as is possible con- 

 sistent with retaining any power 

 of motion. We may divide the 

 musculature of the adult female 

 as follows : 



1. Dorsal muscles. — Along either 

 side of the median Ime of the 

 dorsal surface are tw^o bands of 

 longitudinal muscles, the outer 

 band considerably wider than the 

 inner one (fig. 4). 



These bands are curved length-" 

 wise, bemg farther apart at the 

 center and closer together at the 

 ends. The four bands are each 

 broken at the points which repre- 

 sent the dividmg lines between the 

 different body segments, and thus 

 furnish the best, and in some gen- 

 era (Basanistes, Clavella, etc.) the 

 only, evidence of segmentation. 

 According to this evidence the 

 body of the female of AchtJieres is 

 made up of a cephalothorax, which 

 is a fusion of the head and first 

 thorax segment, and a trunk, 

 which is made up of three thorax 

 segments, a genital segment, and a one-segmented abdomen. The 

 inner pair of muscle bands start from a common pomt of attachment 

 at about the center of the dorsal surface of the cephalothorax. They 

 diverge until they reach its posterior margin, run approximately par- 

 allel through the second and third thorax segments, and converge in 

 the fourth segment, meetmg again at its posterior margm. In the 

 genital segment and in the abdomen there is but a single fused 

 muscle band along the median line. A similar fusion takes place on 

 the ventral surface, this time between the components of the right 

 and left pairs. 



Fig. 4.— Dorsal muscles of Achtheres am- 

 bloplitls. 



