TUBE-MASONS. 315 



case-building caddis larvae of fresh waters, and the 

 tube-masons, or tubicolous annelids of the sea. 

 There are some, perhaps, who would call it mimicry 

 on the part of one or the other, although unjusti- 

 fiably ; whilst some would blame us, on the other 

 hand, for recognising any analogy between them. 

 This is a point we are not anxious to discuss, 

 although a comparison of the two forms of cases 

 would be strongly suggestive, even if nothing more. 

 The marine tubes, or cases, are constructed by anne- 

 lids as a protection, and for the most part by a 

 particular group of Tubicolous annelids, although 

 even to this rule there are exceptions, for a few of 

 the Rapacious annelids (such as Northia tubicola 

 and Nereis diversicolor) construct and live within a 

 tube. Beyond these we are unacquainted with other 

 tube-marine masons which have any claim to recog- 

 nition in this chapter. 



Sir Wyville Thomson mentions a curious little 

 shell-fish (Dacrydium vitreum) dredged from a depth 

 of 2,435 fathoms, "which makes and inhabits a 

 delicate flask-shaped tube of foraminifera, sponge 

 spicules, coccoliths, and other foreign bodies, 

 cemented together by organic matter, and lined 

 by a delicate membrane." * In colour it was a 

 fine reddish-brown dashed with green. 



1 " Depths of the Sea," p. 465. 



