TEGUMENTARY APPENDAGES. 



19 



tissue, which envelops the forceps when closed ; and this apparatus is mounted on a bulging 

 body of a similar substance, which crowns the round, flexible, and contractile peduncle, 

 sometimes simple, sometimes branched, each branch havmg a similar termination. I 

 could detect no evidence of vibratile cilia on their stalks ; but there appeared to be ciliary 

 motions within the blades. When the star-fish is alive, the Pedicellaria are continually in 

 motion, opening and shutting their blades with great activity ; but when cut off, they seem 

 to lose their power." The Pedicellarice observed on certain Echinodermata have been most 

 carefully examined by Sars,^ and I shall enrich this branch of the subject with that accom- 

 plished naturalist's observations on these remarkable appendages of the tegumentary 

 membrane. 



" In examining Echinus sphoira,'' says Sars, " I found upon it all the three sorts of 

 Pedicellaria described by Miiller, viz., P. tridens, P. triphylla, and P. glohifera. Besides 

 what Miiller states in regard to P. tridens, I will make the following remarks : — Internally, 

 there is a hard stem, which is enclosed by a strong, transparent skin, like a sheath. It is 

 thickest at the upper and lower ends, and reaches from the neck, as it is called, to the base, 

 where it, remarkably enough, is fixed and jointed to an exceedingly small barb projecting 

 from the sea-urchin's shell. This circumstance, which is invariable in the Pedicellaria, 

 seems not to have been sufiiciently attended to. The three teeth are concave on the side, 

 turned inwards, angular, and furnished with small teeth on their edges. They are hard 

 and calcareous ; when viewed through a microscope, they are seen connected with very 

 small globules arranged in rows. The stem is also calcareous, yet it can be slightly bent 

 without breaking. The neck is nearly as thick again as the stem ; it is fleshy, transparent, 

 and very flexible. 



" The motions observed in the Pedicellarice, when irritated^ are that the teeth close and 

 squeeze pretty firmly ; in this way, by inserting the point of a pin between them, after 

 the Pedicellaria was torn off, I could draw it out of the water ; further, that the neck 

 bends and inclines to all sides, and can even contract a little, in doing which transverse 

 wrinkles are formed on it ; and, lastly, that the stem, itself inflexible, may bend along 

 with the whole Pedicellaria to the side. The form called Pedicellaria glohifera by 

 Miiller has a head consisting of three outspread flaps, standing nearly horizontally. Each 

 of these flaps is oval, very convex externally, and concave internally, and at the upper end 

 slightly indented, and provided with a sharp point, somewhat bent, Erom the indentatioii 

 runs a raised stripe or rib longitudinally downwards through the flap. On the inner side 

 of these flaps, at their base, is seen an oval and apparently calcareous leaf. 



" The stem, which is similarly constituted with that of P. tridens, proceeds directly 

 from the head (there is no neck in this species), is small above, and thicker below, until at 

 the bottom it completely fills the hollow of the sheath which encompasses it. 



^ ' Ueber die Entwickelung der Seesterne.' — Miill. Arch. 1842, p. 330. 'Ueber die Entwickelung der 

 Seesterne.' — Wiegm. Arch., 1844, ii, p. 169, fig. 



