344 EVENIXGS AT THE MICROSCOPE. 



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 

 excessive 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 I 

 wish specially to direct your attention : yet it is necessary 

 that I say a preliminary word about the former. Ordi- 

 narily the tubes of these worms are formed of the fine 

 impalpable earthy matters (clay, mud, ifcc), held in sus- 

 pension in the sea, incorporated with a chitinous secretion 

 from the body of the animal; and therefore the surface of 

 the tube is always rough and opaque. But in this indi- 

 vidual case, the water in the vessel, probably owing to its 

 habitual stillness, not holding in suspension the particles 

 of mud that ordinarily enter into the composition of the 

 tube, the latest formed portion is composed of pure trans- 

 parent cJiitine, without any perceptible earthy element. 

 This clear terminal portion of the tube you may perceive 

 to be occupied by a curious parasite. About twenty 

 bodies, having a most ludicrously-close resemblance to 

 the human figure, and as closely imitating certain human 

 motions, are seen standing erect around the mouth of the 

 tube, now that the Sabella has retired into the interior,, 

 and are incessantly bowing and tossing about their arms 

 in the most energetic manner. 



