ON CHJITOBRANCHUS. 85 



regularity about thisj and I am inclined to believe that these 

 get more or less injured in the ''burrowing." The length of 

 the processes relatively to the size of the body may be judged 

 of from an examination of fig. 1. 



These processes are obviously branchial in function. The 

 structure of one of these branchial processes is shown in fig. 2. 

 Each is virtually a hollow prolongation of the body wall ; the 

 coelomic corpuscles may occasionally be seen pushed out into 

 it. The epidermis is bounded externally by a distinctly visible 

 cuticle, through which project very fine cilia — so fine that they 

 might easily escape notice but for the commotion which 

 they create among particles of mud in the water. At the 

 extremity are a few stiff processes, doubtless sensory in 

 function. 



Into each of the longer processes (about the first fifty) runs 

 a loop of the lateral vessel (see below, circulatory system). 



Entirely contained within each process are all, in the case of 

 the more anterior, or some in that of the more posterior, pro- 

 cesses of the setae belonging to the dorsal bundle ; so that in 

 the anterior portion (about thirty segments) of the worm no 

 dorsal setse project freely outside the body wall, while in the 

 region immediately following (about thirty segments) two at 

 least of the dorsal setse do not freely project, while one seta 

 of the dorsal bundle does so project, and in the remaining 

 portion of the body all the setae project. 



There are no muscular structures in the branchial pro- 

 cesses, which are kept fairly rigid, and are moved by the 

 dorsal setse, and thus serve the worm as locomotor organs. 



The seta bundles are placed in four rows — two ventral rows 

 and the two dorsal rows mentioned above. The dorsal seta 

 bundles commence in the same segment as do the ventral seta 

 bundles, i.e. the second body segment. Two kinds of setae 

 occur in the dorsal bundles : the one kind is the straight capil- 

 lary seta shown in fig. 5 ; they vary in length ; in the anterior 

 segments they are very long. The seta drawn in fig. 5, if in- 

 tended for one of the longest, should have been drawn double 

 the length it is, to be on the same scale as the setae drawn in 



