ZOOPHYTES. 395 



tip of each bears a dark purple spherule. That of the 

 anterior filament on each side is much larger than the 

 rest, and forms a stout, globose, nearly black ball ; the 

 others diminish to about the twelfth on each side, where 

 they disappear. These balls are placed on the inner or 

 upper face of the filaraent-stem, at the point where the 

 pectination ceases, the stem itself being continued to a 

 slender point beyond it, and constituting the " short 

 hyaline appendage" of Montagu. From their great 

 resemblance to the tentacle-eyes of the Gasteropod 

 JMollusca, I have little doubt that these are organs of 

 vision. If so, the profusion with which the Sahella is 

 furnished in this respect may account for its excessive 

 vigilance ; which is so great, that not only will the in- 

 tervention of any substance between it and the light 

 cause it to retire, but very frequently it will dart back 

 into its tube almost as soon as I enter the room, even 

 while I am ten feet distant. 



It is not, however, to the tube, nor to the w'orm, 

 that I wish specially to direct your attention : yet it is 

 necessary that I say a preliminary word about the for- 

 mer. Ordinarily the tubes of these worms are formed 

 of the fine impalpable earthy matters (clay, mud, &c.) 

 held in suspension in the sea, incorporated with a chiti- 

 nous secretion from the body of the animal ; and there- 

 fore the surface of the tube is always rough and opaque. 

 But in this individual case, probably owing to the habit- 

 ual stillness of the water in the vessel not holding in 

 suspension the particles of mud that ordinarily enter 

 into the composition of the tube, the latest-formed por- 

 tion is composed of pure transparent chitine., without 

 any perceptible earthy element. This clear terminal 

 portion of the tube you may perceive to be occupied 



