238 AMPHITRITE. 



One occurred vertically inverted, being reversed with the orifice down- 

 wards. A specimen of this animal had established itself in the cavity of 

 an old shell, occupied by the Ascidia intestinalis, covering an inch of the 

 tube. The shell was sawn asunder to liberate the Amphitrite, and the 

 tube, thick and dark, slit up to dislodge it entire. This being accom- 

 plished, the animal produced a new and transparent sheath, in twenty- 

 four hours, corrugated and strengthened near the orifice. As specimens 

 seem largest where best protected, this subject was old. 



Gentle pressure upwards always induces the Amphitrite bombyx to 

 quit its tube. 



It is a very timid creature and impatient of light. On the slightest 

 shock, or on interception of the light, the plume collapses, which is ac- 

 companied by instant retreat and closing the orifice of the sheath. The 

 rise of the tenant is slow, with a partial revolution during ascent, per- 

 haps to avoid deranging the order of the plume. But, instead of uni- 

 formly disappearing on alarm, it frequently endeavours to quit its dwell- 

 ing ; and, when the water becomes stale, the body protrudes very far, as 

 if the animal would depart. The facility of forming a new sheath, ren- 

 ders the loss of the old one the less inconvenient. When entirely dis- 

 lodged, the plume expands much more than when the sheath is occupied, 

 the branchiae remaining some time displayed like the radii of a circle. 

 Plate XXXI., fig. 2. 



The branchial apparatus is united to the body by a very thin skin. 

 A specimen, while merely crawling in a vessel, lost the plume entire, the 

 lower part of which, or neck, resembled a complete opening. 



As in the Amphitrite ventilabrum, the branchiae of this species aug- 

 ment in number with age. 



Perpetuation. Of two specimens obtained in the middle of August, 

 one was very turgid. Both formed transparent sheaths, and in three 

 days, a vast profusion of many thousand white specks strewed the bottom 

 of the vessel, amidst the thinnest gelatinous matter. Where most abun- 

 dant, they were of the faintest carnation. Under the microscope, these 

 specks proved to be spherical. They were solid, consisting of a dark and 

 irregular central nucleus, invested by transparent albumen. In one the 



