ON THE BEHAVIOR OF TUBICOLOUS ANNELIDS. 73 



POMATOCERAS TRIQUETER. 



This, with an undetermined species of Serpnla, are tubicolous 

 annelids which much resemble in general aspect of size, structure 

 and behavior, Hydroides dianthus. Indeed in almost every par- 

 ticular they might have been substituted for the latter species 

 without marked changes of results. In general habitat the two 

 species arc much alike and often found growing on the same sub- 

 Mr.it urn. Pomatoceras is rather larger, and its tubes are charac- 

 teri/ed liv rather sharp triangularity with the dorsal angle form- 

 ing a sharp crest along the entire tube. Mo attempt will be made 

 to go into details as to matters of behavior, since as already 

 suggested, they show the same reaction phenomena as those 

 given in tin- accounts of Hydroides dianthus, and tin- growth 

 aspects are <|i' % as erratic. For the most part the tubes adhere 

 cloM-|\ to tin- substratum, and in some cases they a<lju-t thcin- 

 sel\e- \\itli -in h nicety to grooves or similar depressions that one 

 might gin -- ilit-\ wen- under the control of some such stimulus a- 

 thigmotaxi- or stereotropism. But when one com*- to examine 

 an\ i on-idt -rable number of specimens he soon finds that in 

 l>\ tar the larger number there is absolutely no Mich adjuM- 

 ment. The -ame is the case with Hydroides. Now and then a 

 s|)ci imi-ii mav In- found on a shell of Pecten in \\hich there i- a 

 verj tine illustration of such appearance, the creature ha\ing 

 kept \er\ i lo-rly and exactly in the radial groo\- ,,| th,- shell. 

 Hut on the same shell may now and then be found another 

 specimen \\liich has grown directly across the- grooves; and 

 ol course \>\ far the larger number have al>-"lute!v no -nnblance 

 oi -neh re-ponse. The conclusion is therefore forced upon one 

 that the operation of any such factor must be, i! not ulmlly nil, 

 \et ot onl\ incidental significance in behavior. 



Again, in habitat one finds in the Mediterranean species the 

 same \\ide r.m-easin those of Woods Hole. 1 have dwelt upon 

 tlii- |)oint \\ith some emphasis in a lormer pa|>er ('oi), |>p. 

 i^j $). and need only refer to the matter in thi- connection by 

 \\a\- of further emphasizing a point which I regard of considerable 

 significance. The growth of these organisms indiscriminately 

 on a large \arietv of substrata, rock-, shells the latter both 

 dead and living nets, crabs, lobster^, etc., i- it-elf of no small 



