508 



RADIATES : ACALEPHS. 



Fig. 493- 



SUB-SECTION I. 



THE ORDER OF CTENOPHOR.E, OR BEROID MEDUSJE. 



THIS Order contains more or less spherical or ovate 

 jelly-fishes, which have the body built of eight homologous 

 segments bearing eight rows of locomotive appendages 

 more or less distinctly indicated. Agassiz enumerates 

 about seventy species, which he distributes among four 

 sub-orders, twelve families, and over thirty genera. 



CvDiPPiDjE. This Family embraces Pleurobrachia and 

 allied genera. 



The Genus Pleurobrachia has the body nearly spherical 

 or slightly elongated and compressed, the locomotive ap- 

 pendages extending from near 

 the margin of the mouth, in 

 eight rows, towards the oppo- 

 site centre. 



Pleurobrachia rhododactyla, 

 Ag., is common on the north- 

 east coast of North America, 

 and has received very special 

 attention from Agassiz, who 

 says, that, " when active, it 

 hangs out a pair of most re- 

 markable appendages, the struc- 

 ture and length and contractil- 

 ity of which are equally sur- 

 prising, and exceed in wonder- 

 ful adaptation all I have ever 

 known among animal struc- 

 tures. Two apparently simple, 

 irregular, and unequal threads 

 hang out from opposite sides 

 of the sphere. Presently, these 

 > Ag appendages may elongate, and 



