CHAP, xi POLYCHAETA HABITS 285 



such as granite, form the shore line, for the chalk or limestone 

 wears away more quickly, and exposes to destruction the worms 

 which may have sheltered in its crevices: further, it does not 

 give so permanent a place of attachment to seaweeds, on which 

 many Polychaetes feed. The calcareous rocks, too, are more 

 likely to be traversed by springs of fresh water, which is not 

 to the taste of the worms. The sand resulting from the destruc- 

 tion of the rocks, whether hard or soft, is of itself unsuitable to 

 the majority of worms, which are most abundant where mud 

 containing decaying vegetable matter is mixed with the sand : 

 this, which gives a firmer consistency to the soil, so that the 

 burrows retain their form better, supplies food for the burrowers. 



General Habits. The division of the Polychaetes into the 

 " Errantia " or free-swimming and wandering forms, and " Seden- 

 taria " or tubicolous and sedentary forms, is a misleading mode of 

 classification, for as a matter of fact only a comparatively few 

 forms are really free-swimming throughout life ; the majority, 

 even if they do not form definite tubes, burrow galleries for 

 themselves in the soil, and these burrows are in many cases only 

 rarely left ; this is true of both groups. Amongst the " errant " 

 Polychaetes nearly all the Eunicidae secrete a parchment-like tube, 

 and some Polynoids form mud tubes. Among the "sedentary 

 worms " there are forms which merely burrow ; while Myxicola 

 readily leaves its gelatinous tube and swims freely ; Pectinaria 

 carries its house with it as it moves about, and Polycirrus, a 

 Terebellid, does not form any tube at all. 



Owing to their sedentary habits, quite a representative collec- 

 tion of genera may be made, especially at a spring tide, at any 

 seaside place which is provided with a sandy shore, and with 

 rocks and seaweed. The larger species, however, require to be 

 dredged, and the best time is at night, for then many forms 

 which during the day are concealed in their burrows, will be 

 issuing forth to obtain food. 



It may be useful to give instances of worms occurring in 

 various situations between tide-marks. Throughout pretty well 

 the whole of the area left uncovered by the tide, even up to nearly 

 high- water mark in many parts of the coast, the cylindrical 

 " castings " of sand and mud, forming little heaps, indicate 

 the burrows of Arenicola, the common " lug- worm " ; these " cast- 

 ings " have passed through the worm's body, having been 



