MANUAL OF NATURAL HISTORY. 165 



externally with horny plaits, resembling those on 

 the carapace of a Tortoise ; in the Boltenia of 

 Savigny, the body is globular and placed on a long 

 peduncle ; in Clavellina the individuals composing 

 the general mass are connected by creeping, root- 

 like prolongations ; in the Botrylli they are ad- 

 herent, side by side ; in the genus Polyclinum they 

 are placed at unequal distances from a common 

 centre ; in Distoma the individuals are in one or 

 two ranks, at unequal distances from the common 

 centre ; while in Diazona they are arranged in con- 

 centric circles. The Pyrosomes, having the animals 

 united together in whorls, forming a common cylin- 

 drical tube, float freely about the warmer parts of 

 the ocean, and are frequently met with in incre- 

 dible numbers ; at night these tubular brotherhoods 

 are vividly phosphorescent, and exhibit a striking 

 effect as they move vertically through the water. 

 The Salpians are also remarkable animals, occurring 

 under two distinct forms, being met with sometimes 

 associated in long strings, at others, solitary and 

 isolated ; the solitary kinds, as discovered by Cha- 

 misso, not being specifically distinct from those 

 united in chains, but either their parents or their 

 progeny. The Pelonaians resemble the Sipunculi 

 among the Echinoderms, and differ from the Asci- 

 dians in being bilateral ; in the transverse plaits of 

 their bodies they seem also to present an analogy 

 to the Annulose animals. The very singular genus 

 Appendicular ia, for which we have constituted a 

 family, has been ably investigated by Huxley, who 



