70 SEA-SIDE STUDIES. 



addition to the two imi)ortant uses already assigned to these 

 tentacles, they constitute also the real agents of locomotion. 

 They are first outstretched by the forcible ejection into them 

 of the peritoneal fluid, they are then fixed like so many 

 slender cables to a distant surface ; and then, shortening in 

 theii- lengths, they haul forward the helpless carcass of the 

 worm."* The cai'cass of the worm is by no means so help- 

 less as here described. It is true that the tentacles are 

 employed to drag the animal along. You obsei-ve how that 

 one is crawling up the sides of the glass, and now hangs 

 suspended to the floating weed : but you may also observe 

 him •wriggling about his body with great activity, and by 

 these contractions he is enabled to make progress, even 

 when deprived of his tentacles. 



There is a more serious objection, however, to be made to 

 the passage I have just abridged. Dr Williams — in com- 

 mon Avith most, if not all, anatomists — speaks of the mus- 

 cular parietes of these tentacles. I venture to suggest that 

 there is great inaccuracy in the term ; and that the existence 

 of these nmscles is a jjure assumption, assumed to explain 

 the Contractility of these organs, in the same way as a 

 nervous system is constantly assumed to explain some 

 phenomena of Sensibility, although not a trace of a nerve 

 can be detected by the highest powers of the microscope. 

 The assumption is in each case perfectly needless, and very 

 misleading. It is against all philosopliy thus to assume the 

 existence of a tissue no one can detect, to explain a pheno- 

 menon which may be otherwise explained. Nor is anything 

 * Williams : Iteport, p. 19-1. 



