284 Dr. W.C. M‘Intosh 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 Pl. 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 zn situ. The shaft of the 
hook in the large examples is marked at intervals by trans- 
verse stria. Mr. Lankester’s figurest 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 f. 
* Ann. des Sc. Nat. sér. 3. Zool. tome xiv. pl. 5. fig. 10. 
+ Ann. Nat. Hist. ser. 4. vol. i. 1868, pl. 11. fig. 9. 
{ 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 in a large coloured 
drawing accurately copied from the two figures (Pl. XVIIT. figs. 2 a, 6) ac- 
