30 MARINE WORMS. 



P. propinqua (P. fioccosa of M'lntosh), is short and squat, 

 scarcely an inch in length, while the commensal species run 

 to four and five inches. The common free Polynoe cirrata, 

 which takes the place of this species in northern seas, is 

 characterised by an equal shortness. 



Yet another local species, Polynoe marphysce, is commen- 

 sal ; this time with the great rock worm, Marphysa sanguined, 

 which excavates and lines long tunnels in the rocks so gene- 

 rally round the coasts in these islands. 



There are other British Polynoince known sometimes to 

 be commensal, which here I have not, so far, met with 

 pursuing this habit, viz., Hermadion pellucidum and H. assimile. 

 In the Irish sea I have found the former crawling upon 

 Astropecten, Solaster, and Ophiothrix. Here I have found it, 

 but in a free state, crawling over a tuft of Polyzoa in a 

 coralline pool. H. assimile, found sometimes upon Echinus 

 esadentus, I have never seen in these islands. The Acholae 

 astericola mentioned above is also absent from my list of local 

 annelids, probably because I have not had an opportunity of 

 examining any local Astropecten. 



Several of the Syllidce are, I believe, commensal, but the 

 only one met with here is Syllis (armillaris ?) within the 

 mantle of Ascidia mentula. This is the only case I have seen 

 of direct commensalism between Ascidian and Annelid, but 

 there are several very important instances of an indirect and 

 occasional relationship between these two groups deserving of 

 close attention. 



Downwards, from a little above low-tide mark, the shel- 

 tered surfaces of the rocks in our islands are often literally 

 hidden by closely packed dark red bladder-like Ascidians 

 ( Styelopsis grossularia ) and occasionally at a low horizon these 

 red walls are replaced by masses of shapeless, hueless Ascidia 

 mentula. If we scale off a mass of this Ascidian mantle, at 

 the cost of sundry too-well aimed squirts of salt water from a 

 myriad of miniature nozzles, we find, on close examination, 

 quite a motley assemblage of annelids, comprising far-sundered 

 species, living in tubes meandering in and out among the 

 Ascidian individuals. The worms inhabiting these tubes 

 comprise, among others, Eunice harassii, Lumbrinereis latreillei, 

 Dasychone dalyelli, Sabella saxicava and several Syllidce. 

 Except Dasychone and Sabella these belong to the Errant 

 Annelids, which are as often as not as inveterate tube-builders 

 as the Tubicolous Annelids of our Zoological Text-books — a 

 proof, if it be needed, of the difficulty of framing faultless 

 titles for the various groups of the animal kingdom. 



