CORPUSCLES OF MARINE WORMS. 141 



the setae are much larger than the rods, are blunt at one 

 end and pointed at the other, and have well marked 

 characteristics which differ entirely from the well defined 

 bow-shape of the rods. That the bow-cells may be cells 

 of some fixed tissue seems equally unlikely. A diagram 

 of a bow-cell and a diagram of a smooth muscle-cell, it is 

 true, present a general resemblance, and it was suggested 

 to me that the contraction of the muscular element in 

 the isolated cell might produce the characteristic arcuate 

 shape ; this, however, is quite impossible, seeing that the 

 rods are rigid when rolled over in a fresh preparation, by 

 means of gently tapping the coverslip, and also in view of 

 the fact that the rod is unaffected by caustic potash, and 

 is therefore not a muscular fibre, but is of a similar nature 

 to chitin. That the bow-cells have been accidentally 

 isolated from any other fixed tissue seems equally unlikely. 

 What fixed tissue shows cells with long waving filamentous 

 pseudopodia distinct from cilia ? Only alternative conclu- 

 sions remain to us, either that the problematical body is a 

 parasite differing from any known parasite, or that it is a 

 corpuscle. 



It may be said that in fairness, one should add, " dif- 

 fering from any known corpuscle." But it will have 

 occurred already to the reader that the bow-cells have 

 much in common with the well-known rod-cells of the 

 Polychsete, Ophelia radiata (fig. 5). Ever since Claparede 

 discovered and described these remarkable bodies, they 

 have been regarded as unique, and the opinions that they 

 are parasites or corpuscles have been variously held. 

 Schaeppi, however, has shown conclusively that they are 

 corpuscles.* 



The rods in the corpuscles of Ophelia are so large 

 as to be visible to the naked eye. They are of a deep 



* Schaeppi, Jen. Zeitscli. f. Nat. Wiss., 1894, p. 246. 



