SECT. vi. ECHINODERMATA. i8<j 



Echinodermata Synaptidce. 



The Synaptidse are five-sided creatures, similar in 

 structure to the Holothuriae, though more worm-like. 

 The whole order, which consists of the two genera of Syn- 

 apta and Chirodota, have twelve calcareous plates round 

 the mouth, five of which are perforated for the passage 

 of the vascular water canals, which convey the liquid for 

 the protrusion of the feet. 



The calcareous particles imbedded in the skin of 

 the genus Synapta are anchor-shaped spicules fixed to 

 elliptical or oval plates, 

 (fig. 144). The plates 

 are reticulated and some- 

 times leaf-shaped, and the 

 flukes of the anchors are 

 either plain or barbed. 



All the anchors are fixed Fig 144 Skeletou of Synapta 



transversely to the length 



of the animal, lying with great regularity in the inter- 

 spaces of the longitudinal muscular bands. Some- 

 times a thousand anchors are crowded into a square 

 inch, each elegant in form, perfectly finished, and ar- 

 ticulated to an anchor-plate, whose pattern as well as 

 that of the anchor itself is characteristic of the species 

 to which it belongs. In the Synapta digitata, which 

 has four fingers and a small thumb on each of its 

 twelve oval tentacles, the anchors are but just visible to 

 the naked eye ; 9 in all the other species they are micro- 

 scopic. Besides the anchors, the skin of the genus 

 Synapta contains innumerable smaller particles, 'miliary 

 plates,' which are crowded over the muscular bands. The 

 muscular system of the Synapta digitata is so irritable 

 that, on being touched, it divides itself into a number of 



9 Messrs. Woodward and Barrett on the Synapta. Trans, of Zoological 

 Society, London. 



