74 MARINE ANIMALS OF MASSACHUSETTS BAY. 



into points of a conical or cylindrical shape. This polymorphism 

 among the Tubularians is another evidence of the relation be 

 tween the Siphonophorae, or floating Hydroids, and the fixed 

 Hydroids. 



Hybocodon. (Hybocodon prolifer AG.) 



Among our Medusae derived from a Tubularian stock is the 

 Hybocodon, viz. the hunchbacked Medusa (Fig. 102), a singular 

 little Jelly-fish, odd and unsymmetrical in shape, as its name 

 indicates, and interesting from its relations to one of our floating 

 communities, the Nanomia, presently to be described. Instead 

 of the evenly proportioned bell of the ordinary Medusas, the 

 Hybocodon has a one-sided outline (Fig. 102), one large tentacle 

 only being fully developed, while the others remain always abor 

 tive, so that the whole weight of the structure is thrown on one 

 half of the bell. Upon this large tentacle small Jelly-fishes, 

 similar to the original, are produced by budding, this process 



Fig. 102. 



Fig. 103. 



going on till ten or twelve such Jelly-fishes (Fig. 103) may be 



seen suspended from the tentacle. Up to this time it has re- 

 Fig. 102. Unsymmetrical free Medusa of Hybocodon ; ro chymiferous tubes, v proboscis, s circular 



tube, m young Medusae at base of long tentacle t. (Ayassiz.) 



Fig. 103. Medusa bud of Hybocodon ; a base of attachment, o proboscis, c circular tube, d young 



Medusae at base of long tentacle t. (rfyassiz.) 



Fig. 104. Single head of Hybocodon Hydroid ; a stem, d Medusae buds, o tentacles round mouth. 



(Agassiz.) 



