284 Dr. W. C. Mcintosh on the Boring of certain Annelids, 



trace of the " trichocysts." M. de Quatrefages*, again, in his 

 remarks on the respiration of the Annelids, refers to a drawing 

 of the tentacle of a Polydora^ which may or may not be this 

 species. He shows the ciliated region to be cellular, but does 

 not notice crenations. 



On the tentacles of several were the curious parasitic forms 

 represented in PI. XIX. fig. 3. They were attached by a short 

 stalk, and, when set free, moved rapidly through the water by 

 the aid of their cilia, which in their fixed condition were next 

 the tentacle. 



The fifth body-segment of the worm has the characteristic 

 strong hooks (PI. XVIII. fig. 2), which are accompanied by the 

 peculiar bristles with spear-shaped heads (fig. 3), besides the 

 minute dorsal fascicle of the ordinary structure. The tip of 

 each of the first series is strongly curved ; and towards the 

 concave side thereof a spur projects, apparently with a twist 

 backwards and ventrally ; and hence, if the organs are sepa- 

 rated and pressed between glasses, this spur in not a few cases 

 almost escapes observation ; this is especially the case in spirit 

 preparations. In the larger southern examples the spur is less 

 visible than in the smaller, as the hook under pressure assumes 

 a position which hides the projection ; it is very evident, 

 however, when the hook is viewed in situ. The shaft of the 

 hook in the large examples is marked at intervals by trans- 

 verse stri^. Mr. Lankester's figures t may be taken as the 

 representatives of altered bristles from specimens in which 

 they have been subjected to some morbid influence, either due 

 to the nature of the habitat (calcareous rock) or otherwise. 

 Other specimens from the same rock show the ordinary struc- 

 ture with the single spur beneath the tip. In some of the 

 altered specimens the spear-shaped bristles accompanying the 

 hooks are absent. Mr. Alex. Agassiz has given a better view 

 of their structure, though he does not refer to the spear-shaped 

 bristles which accompany them. In the majority of the spe- 

 cimens from St. Andrew's three of the hooks were well deve- 

 loped, the first being the longest, and the fifth and sixth rudi- 

 mentary but nevertheless showing the secondary fang or spur 

 even more distinctly than the others. In larger examples from 

 Cobo Bay, Guernsey, and the southern shores of England, 

 these hooks are more numerous J. 



* Ann. des Sc. Nat. ser. 3. Zool. tome xiv. pi. 5. fig. 10. 



t Ann. Nat. Hist. ser. 4. vol. i. 1868, pi. 11. fig. 9. 



X At the late meeting of the British Association, Mr. Lankester^ while 

 at once admitting the erroneous condition of his own published drawing 

 of the hooks, denied the accuracy of mine as exhibited m a largo coloured 

 drawing accurately copied from the two figures (PI. XVIII. figs. 2 a, h) ac- 



