24 MICROSCOPICAL STUDIES. 



from the body are joined two branch limbs, one directed inwards, 

 the other outwards, respectively endopodite and exopodite. Each 

 again is divided into 3 short joints, bearing setcv or stout hairs 

 definitely placed (PI. iv, Fig. 12). The 1st pair differs from the 

 others in possessing one hair less on the distal joint of the exopodite. 

 All the setas of the feet are finely plumose. The fifth pair of feet, 

 present only in the female, is very different, as each foot consists 

 merely of two short weak joints, bearing at the termination a couple 

 of slender hairs. 



The abdomen consists of 4 joints (Fig. 10, 1, 2, 3 & 4), ending in 

 a forked tail. Each fork bears 1 slender and 5 stout bristles in 

 the position shown in Fig. 11. Lubbock erred in writing " upon the 

 fourth candal seta (counting from the outside) is another, rather 

 smaller than the other five." In reality it arises from the tail fork 

 in the same way as its fellows, but being very slender, a mistake 

 is very liable to occur. Mr. I. C. Thompson has apparently over- 

 looked this slight hair in his diagnosis of the species as he says 

 " 5 setae to each furcal segment " (6). 



Muscular System. By selective staining, I have been fortunate 

 in being able to make out very clearly the principal arrangements 

 of the muscles. A glance at Figs. 10 and ] 1 will show how immensely 

 powerful this tiny creature (female 3 mm. long ; male 2*25 mm.) is in 

 proportion to its size. This is apparently against the idea of the 

 generally parasitic life of this animal, for such life in general leads to 

 partial atrophy of the muscles. Still it does not dispose of the 

 suggestion there may be compensating causes. 



To return. The largest muscles are found within the carapace, 

 lying longitudinally ; four pairs arranged as in Figs. 10 and 11. The 

 two upper or dorsal pairs are used in straightening or extending 

 the body, extensors ; the other two pairs for bending or flexing, 

 i.e. flexors. Each of the following body rings or segments possesses 

 but one pair of extensors and the same number of flexors, modified 

 however in the abdomen by the extensors of the first and second 

 segments, and both the extensors and the flexors of the third and 

 fourth being respectively wholly or in great part coalesced. Thus 

 these segments lose more or less their independence of action, the 

 first and second acting in concert in extension, the third and fourth 

 in all movements. To understand well the action of these body 

 muscles we must remember that the axis of movement between 

 adjoining body rings lies transversely across the body a little above 

 the articulation of the feet, so it is obvious that a pull below such 

 axis, will bring the rings together on the under side, producing 

 flexion ; conversely, if above, the opposite, i.e. straightening will 



