HABITS OF THE ONUPHIDJE. 317 



closing the mouth of the tube in different ways ; for 

 example, Serpula, Sjrirorbis and Sabellaria by opercula or 

 structures connected with their ow T n heads ; Sabdla, by the 

 collapse of the lately formed mouth of the tube ; 

 Pectinaria, by a sand, mucus-made, minutely perforated 

 appendage to the smaller end of the tube (a fact first 

 noticed, I believe, by Dr. Pierre Fauvel) ; Terebella 

 littoralis, to some extent, possibly, by the falling together 

 of the beautifully filamented fans with which it decorates 

 the mouth of its tube ; Sabella saxicava (often, but not 

 always, says Soulier), by the curious coiling up of its tube, 

 like a watch spring, and uncoiling like the young frond 

 of a fern (a sight which I first had the good fortune to 

 see) ; but the defensive mechanism of the Onuphidae is to 

 me a new and exceptionally interesting method, and I am 

 greatly indebted to Prof. Herdman, who, on one of the 

 Liverpool dredging expeditions, first drew my attention to 

 these worms, and to Dr. Allen and Mr. A. J. Smith, of 

 the Plymouth Laboratory, who have kindty procured for 

 me the living specimens with which I have recently 

 worked. 



EXTLANATION OF PLATE. 



Pig. 1. Tube of Hyalincecia tubicola, natural size, from 

 a photograph, showing Y-shaped, anterior 

 valves, v, and zigzag, posterior valves, v'. 

 Intermediate markings are traces of old valves 

 which have been removed by the worm when 

 lengthening its tube to make more habitable 

 space. 



Pig. 2. Diagram, showing action of the protective valves, 

 v, v, at the anterior end of the tube of 

 Hyalinozcia tubicola. The arrow indicates the 

 inrush of water closing the valves. They are, 

 of course, raised and opened by pressure of the 

 animal or water in the opposite direction. 



