532 CRESSWELL SHEARER. 



The solenocytes of the first nephridium are quite like those 

 of the following uephridia in appearance^ although a number 

 of observations have led me to believe that they are somewhat 

 finer and more pin-head -shaped in outline. Unlike the 

 solenocytes of Polycheets, it is difficult to see the lumen of 

 their solenocyte tubes^ although their flagella can be traced a 

 little way up the narrow refractive stalk which attaches the 

 solenocyte to the end of the nephridial canal ; neither can the 

 end of this tube be seen projecting into the nephridial canal 

 as in some Polychtets. In the head of each solenocyte is a 

 clear refractive dot ; this is so regular in shape and size as 

 to preclude its being a nucleus. Each solenocyte sends a 

 single flagellum down the canal of the nephridium, so that 

 the accumulated flagella of all the solenocytes form a mass 

 which almost fills the lumen of the canal. The waves of 

 ciliary motion starting in the solenocytes travel progressively 

 down to the ends of their flagella. As already mentioned, I 

 believe each flagellum extends the length of the nephridial 

 canal (fig. 6). In cases when the ciliary motion has almost 

 ceased and the movements of the flagella are consequently 

 slow, the wall of the canal is exposed from time to time as the 

 flagella move from side to side ; it is then seen to be bai'e 

 without any trace of the insertion of cilia (fig. 5). At the 

 same time the individual lashes of the flngellum can be dis- 

 tinctly seen, and in some instances traced to their respective 

 solenocytes. As each lash beats backwards and forwards in 

 the canal it causes its solenocyte to vibrate with it in the bod}"- 

 cavity space, and as the waves of motion pass down the 

 flagellum in a metachronous manner the solenocyte vibrates 

 backwards and forwards at each wave. As the solenocytes 

 are inserted on the ends of the nephridial canals in all possible 

 directions with regard to one another their vibrations are not 

 necessarily in the same plane. Sometimes it happens that 

 they are arranged so that a large number of them beat in the 

 same plane, when the whole mass moves together; usually, 

 however, this is not the case, each solenocyte has its own 

 separate motion, and they all appear to beat independently of 



