190 6- 1907.] Lopcpoda living as Messmates with Ascidians. 357 



y.— OBSERVATIONS ON SOME COPE POD A THAT 

 LIVE AS MESSMATES OB COMMENSALS 

 WITH ASCIDIANS 



By THOMAS SCOTT, LL.D., F.L.S., Honorary Member. 

 (.Read Feb. 27, 1907.) 



In two previous papers read before this Society — one in 

 January 1903 and the other in March 1905 — I referred to a 

 number of Copepoda which, in one way or another, are 

 associated with fishes and with various marine invertebrates, 

 as parasites, messmates, or commensals. In these papers I 

 have shown that, in addition to fishes, — all of which now and 

 then become, nolens volens, the hosts or entertainers of many 

 kinds of Copepoda, — such organisms as Sponges, Echinoderms, 

 Annelids, Crustacea, and Mollusca are also called upon to 

 provide food and shelter for not a few of those guests which, 

 in almost every case, may be correctly described as " un- 

 invited." 



As no special mention was made in my two last papers of 

 the messmates of the Tunicata, my observations in this third 

 paper will be confined chiefly to some of those Copepoda that 

 are known to live in the company, and under the shelter and 

 protection, of various kinds of Ascidians. To judge from the 

 number of the organisms sometimes found located upon and 

 within the test of one of the larger Ascidians or Tunicates, 

 one might be led to imagine that the other invertebrata con- 

 sidered the test of an Ascidian to be common property, and 

 had proceeded to carry out the socialistic idea, as far as they 

 could, to its logical conclusion by taking forceful possession 

 both of the outside and inside of the Ascidian's dwelling, — a 

 dwelling which it had built up by its own exertions and for 

 its own convenience. 



Among the trespassers upon the preserves of the Tunicata 

 is the Modiolaria marmorata. This dainty mollusc may 

 frequently be found embedded in the tests of the larger 

 Ascidians, such as, for example, Ascidia (Phallusia) mentula 



