702 CLASS XI. 



connexion to be detected, not at least, according to MILNE EDWARDS, 

 in Polyclinuni. 



Family II. Lucice. Apertures of external covering opposite, 

 terminal. Branchial sac girdled anteriorly by a membranous denti- 

 culate ring, open posteriorly. Several animals aggregated to form 

 a compound body swimming freely, cylindrico-conical, hollow 

 internally. 



Pyrosoma PEKON. 



This genus of compound Ascidice was first discovered by PERON and 

 his fellow-voyagers in the Atlantic ocean under the Tropics, when in 

 a dark night numerous specimens of it appeared to form a broad 

 band of light across the sea. From this phosphoric quality, the 

 name (Fire-body) is derived. At first these compound animals were 

 supposed to be a single animal, and the single individuals of which 

 a Pyrosoma is compounded, to be little tubercles on the surface 

 of the animal. See PERON Mem. sur le nouveau genre Pyrosoma, 

 Ann. du Museum, iv. pp. 437 446. For a more accurate know- 

 ledge of this remarkable genus we are indebted almost exclusively 

 to the investigations of SAVIGNY. The compound body is a much- 

 elongated cone, ordinarily six or seven inches in length, open at 

 one end and at the other closed and bluntly rounded off. The 

 little animals are placed perpendicularly to the axis of the cone, in 

 circles more or less irregular, whilst the posterior openings of their 

 body terminate in the cavity of the cone. The gem, according 

 to the observations of SAVIGNY, is already cloven into four animals 

 even before they are born. This is the commencement of the cylin- 

 der or cone, which may be imagined to be formed of a series of 

 circles or girdles of small Ascidice behind each other of increasing 

 size ; the thinner closed extremity of the compound body is thus 

 the first formed. Consult SAVIGNY 1. cit. pp. 58, 206. 



Sp. Pyrosoma atlanticum PERON, 1. 1. PI. 72, Voyage aux Terres Australes, 

 PI. 30, fig. i ; Pyrosoma giganteum LESUEUR, SAVIGNY Mem. u. PL 4, 

 fig. 7, PI. 11, 23, BLAINV. Malac. PI. 83, fig. 6, Cuv. R. Am., td. ill, 

 Moll. PI. 133; in the Mediterranean: there is still a smaller species in 

 the same sea in which the individual animals are placed in regular circles 

 round the cone; Pyros. elegans LESUEUR. 



Family III. Ascidice. Apertures of external covering not oppo- 

 site, mostly approximate. Branchial sac closed posteriorly. Animals 

 either single, or congregated into a common body, affixed. 



