XI SIPIIONOl'HORA CALYCOPIIORAE 305 



tentacle. The tension on its peduncle thus produced acts as a 

 stimulus on apparently some centre there which causes it to 

 contract. The fish in this way is drawn up so that it touches 

 the sticky mouths of the squirming siphons [i.e. gastrozooids]. 

 As soon as the mouths, covered as they are with a gluey sub- 

 stance and provided with nettle-cells, touch the fish they stick 

 fast, a few at first, and gradually more. The mouths open, and 

 their lips are spread out over the fish until they touch, so that 

 by the time he is dead the fish is enclosed in a tight bag com- 

 posed of the lips of a dozen or more siphon mouths. Here the 

 fish is digested. As it begins to disintegrate partially digested 

 fragments are taken into the stomachs of the attached siphons 

 (gastrozooids). When they have become gorged they detach 

 themselves from the remains of the fish, the process of digestion 

 is completed in the stomachs, and tiio nutrient fluid is dis- 

 tributed. ..." 



In consequence of the very unsatisfactory state of our know- 

 ledge of the life-history of the Siphonophora the classification of 

 the order is a matter of unusual difficulty. 



Sub-Order I. Calycophorae. 



The character which distinguishes this sub-order is the absence 

 of a pneumatophore. 



The colony usually consists of a long, slender, contractile stolon, 

 provided at one end with one, two, or several nectocalyces. Upon 

 the stolon are arranged several groups (" cormidia ") of poly- 

 morphic zooids. 



The nectocalyces have a well -developed velum, four radial 

 canals, and a muscular umbrella- wall. A special peculiarity of 

 the nectocalyx of this sub-order is a diverticulum (oleocyst) fi'om 

 one of the radial canals, containing a coloured globule of oil. 

 The function of this oil-globule is prol^ably similar to that of 

 the pneumatophore, and assists the muscular efforts of the necto- 

 calyces in keeping the colony afloat. One of the nectocalyces of 

 each colony exhibits on one side a deep ectodermic fold, which is 

 frequently converted into a pit. At the Ijottom of this pit is 

 attached the end of the stolon, the whole of which with its 

 numerous cormidia can be withdrawn into the shelter of the 

 pit when danger threatens. The cormidia consist of at least four 



VOL. I X 



