AMPHITRITE. 237 



figs. 3, 4, 5. Besides corresponding coloured spots, several pair of pecu- 

 liar shaped, flattened, transparent organs, endowed with some extension 

 and contraction, and apparently of the same consistence as the cilia, pro- 

 ject from the back of the rib. Fig. 6, a, b, c, stem enlarged. Two stout 

 pointed antennular spines are situate in the centre of the bottom of the 

 plume or funnel, where the converging branchise meet below. These 

 organs are susceptible of prolongation, and have the faculty of transmit- 

 ting particles up the back. Fig. 7, enlarged. 



The plume is proportionally larger and more luxuriant than that of 

 the Amphitrite ventilabrum. It is finely variegated with different shades 

 of brown and yellow. Orpiment orange is the colour which predominates 

 on the body. 



This animal dwells in a tube surpassing its own length, which is not 

 of mechanical construction, but is formed by a spontaneous exudation 

 from its whole body, comprehending the extremities, or from any part 

 of it. When originally produced, it is clear as crystal, completely ex- 

 posing the tenant's external organization, of corresponding figure. If de- 

 prived of the surrounding element, its aspect is somewhat gelatinous, but 

 it seems truly of silken fabric, and becomes quite opaque with age. The 

 upper part is corrugated, darker, thicker, and stronger than the rest, evi- 

 dently for protection of the plume, which is the most delicate part of the 

 creature. The lower extremity is close and obtuse. Plate XXXII., 

 fig. 1. 



The secretion whence the tube is derived, must be accounted very 

 copious, as several tubes can be formed in succession. Whether any 

 share of it is afforded by the plume seems uncertain, farther than as a 

 glutinous matter, overspreading the vicinity, as a preservation of the 

 animal parts from abrasion. 



Contrary to the direction of the tube essential for discharging the 

 mechanical functions of the Amphitrite ventilabrum, naturally vertical, 

 that of the Amphitrite bombyx is usually horizontal. Herein the plume 

 is stationary, it has no such functions to discharge ; nor, although the 

 tube be occasionally vertical, and the plume remains free, is there any 

 revolution, as by the former species. It affixes readily to all substances. 



