130 MARINE INVERTEBRATES 



ORDER SIPHONOPHORA 



FREE-SWIMMING COLONIES 



This order of hydroids consists of free-floating communities 

 and is one of peculiar interest, since it shows in a clear manner 

 the special function of each individual member of the colony, 

 and illustrates better than the foregoing, perhaps, the curious 

 forms of animal life which this class presents. 



GENUS Nanomia 



N. cara. This species is found on the New England coast. The 

 members of the community are arranged along a hollow stem about three 



inches long which opens into 

 every individual. At the top 

 of" the stem is a sac, or float; 

 just below this is a group of 

 swimming-bells which have 

 no manubrium or mouth, and 

 whose sole function is to pro- 

 vide locomotion for the com- 

 munity ; and below these are 

 three sets of zooids, each 

 having a triangular shield 

 and tentacles. The tentacles 

 are longer than the main stem. 

 One of these last groups con- 

 sists of the nutritive members, 

 the mouths of the community, 

 resembling manubriums of 

 swimming-bells out of place. 

 Each one has at the point of 

 attachment a bunch of long, 

 delicate tentacles having pen- 

 dent knobs of lasso-cells. A 

 second group, also with 

 mouths, has shorter tentacles 

 which are carried in spiral 

 coils. The members of the 

 third group have but one ten- 

 tacle each and resemble the 

 float at the end of the stem ; 

 presumably these drop off and 

 produce new colonies. There 

 are also on the lower part of 

 the stem other reproductive 



members, which resemble the 



Adult Nanomia cam. clusters of buds seen on 



