On Stîchocotyle ncphropis Cunninghatn, a parasite of the Ameiiean loljsler. 459 



aod retractor muscles of the pharynx (PI. 29, Fig. 5), by which 

 i'h;iii[,'es in the position of the i)harynx are accomplished. These fibres, 

 like those of the lon^ntudinal muscles of the body-wall previously 

 described, have the nucleus attached upon one side of the contractile 

 filament, as shown in PI. 30, Fig. 10. They frequently differ however 

 from the muscles of the body-wall in having their ends branched. 

 Hy this means they may have a double insertion, as is to be seen in 

 the case shown in Fig. 10b. Additional muscles are found in the 

 suckers and will be treated of in connection with those structures. 



Suckers. 



The number and arrangement of the suckers has been already 

 spoken of. The method of formation of new suckers may next receive 

 attention. 



Cunningham says (p. 274): "The suckers are always more dif- 

 ficult to distinguish at the posterior end of the series, where they are 

 very small, and they evidently increase in number at this end, just 

 as the segments of a Chaetopod." 



In PI. ol. Fig. 22 is shown the appearance of a median sagittal 

 section through the posterior portion of a specimen of Sticliocotyle. 

 It will l)e seen from this figure not only that the suckers are suc- 

 cessively smaller and closer together toward the posterior end of the 

 body, but that they all appear to be derived from a common mass 

 of tissue, which is sharply set off from the general parenchymatous 

 tissue of the body. It seems probable from this that in an early 

 stage in ontogeny a certain cell, or group of cells, was diöerentiated 

 from the rest to become the fundament of the suckers. This mass 

 must have elongated backward to keep pace with the growth of the 

 worm, while at the same time its anterior end became broken up 

 into separate masses, each one of which was converted into a single 

 sucker. 



That the muscles of the suckers are entirely distinct from those 

 of the body-wall, as observed by Cunningham, need occasion no sur- 

 prise when it is taken into account that the material from which the 

 suckers are formed has i>rol)ably been from an early period in the 

 history of the individual entirely distinct from the outer tissue of 

 the body. 



'J'he evident manner of origin of the separate suckers harmonizes 

 with the idea of the close relationship of this species with the Aspido- 

 hothridae expressed by Monticelli ('92). Voeltzkow C88) observed 



3U* 



