328 FRANK E. BEDDARD. 
were nearly always in this position when examined alive. I 
have found, however, by transverse sections, that the bran- 
chial process arises in the middle dorsal and middle 
ventral lines of the body respectively. This is shown 
in the sections represented in fig. 138. The anus is thus 
really dorsal, as in Dero, and there is nothing especially ab- 
normal about its position. But the position of the branchiz 
is very remarkable indeed; a fusion between the branchiz of 
successive segments would produce something like the un- 
paired fins of Vertebrates. It has been suggested, by the 
advocates of the Annelid origin of Vertebrates, that the ap- 
proximation and fusion in the mid-dorsal line of the notopodia 
of the parapodia may have produced the dorsal unpaired fin ; 
in Branchiura we have the unpaired character of the pro- 
cesses of the body already established. 
When Chetobranchus is in motion the branchial pro- 
cesses iaturally move with the setz ; there is, so far as I could 
ascertain, no intrinsic movements of the branchiz themselves, 
which indeed do not appear to be provided with any muscles, 
as Professor Bourne has rightly stated. They are kept rigid 
by the sete. In Branchiura the individual movement of 
each branchia can be readily seen. The whole of the posterior 
end of the worm’s body was in continual movement, while the 
anterior end remained quiet. The body itself oscillated to 
and fro with a peculiar vibratory movement: this of itself 
caused a fluttering of the branchize; but in addition to this 
each branchia moved independently, writhing about like the 
cirri and tentacles of some Polycheta. The branchiz not only 
moved from side to side, but became alternately extended and 
retracted, so that their length was much greater at one time 
than at another. Hence it is difficult to give any measure- 
ment that would apply accurately to the branchiz of the living 
worm. After treatment with corrosive sublimate and alcohol 
the length of the longest branchia was generally rather less 
than the diameter of the body ; during life it was frequently 
the other way about. The branchie frequently present the 
wrinkled appearance shown in the accompanying figure (Pl. 
