388 EVENINGS AT THE MICROSCOPE 



ing in this tank a specimen of that rather rare and very 

 interesting Sabella, the Amphitrite vesiculosa of Montagu. 1 

 You see it is a worm, inhabiting a sort of skinny tube, 

 much begrimed with mud, about two inches of its length 

 being exposed; the remainder, or about as much more, 

 being concealed among the sand and sediment of the 

 bottom. 



A beautiful object is presented by the gill-fans of this 

 worm. These organs are always elegant, whatever species 

 of the genus is before us; but here, in addition to the 

 charm of the slender filaments, so delicately fringed with 

 their double comb -like rows of cirri, the 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 filament- 

 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 Mollusca, I have little doubt that these are 

 organs of vision. If so, the profusion with which the 

 Sabella is furnished in this respect may account for its ex- 

 cessive vigilance; which is so great that not only will the 

 intervention 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 worm, that 



1 "Linn. Trans.," xi. 19. 



