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 Polydinum 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 

 associatec 1 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 

 Appendicularia, for which we have constituted a 

 family, has been ably investigated by Huxley, who 



