TEE GROWTH OF JELLY-FISHES. 579 



tliey may be numbered by hundreds or even thousands, form one 

 continuous organism. 



The stomach of each member of the colony is directly con- 

 tinuous with the hollow roots, and, through these, with the body 

 of every other member, and any food which is captured and di- 

 gested by one, serves to nourish all, since it circulates everywhere 

 through the roots, as water flows through the mains to all the 

 houses in a city. . * 



The whole is the result of multiplication by buds, and all the 

 members are derived from one, which hatched from an Qgg, 

 and, fastening itself to a shell, founded a new colony. A new bud 

 may grow out anywhere, from the roots, and as the current of 

 food which is always sweeping by provides it with ample nour- 

 ishment, it grows quickly, and the repetition of the process 

 of budding brings about a rapid increase in the size of the com- 

 munity. 



The existence of a mechanism for propelling food to all its 

 members facilitates the division of labor, or polymorphism, which 

 is the most remarkable characteristic of these hydroid communi- 

 ties. In human history the growth of agriculture has supplied 

 the first need of all men, abundant food, by the labor of a few, 

 and has thus rendered division of labor possible, and has per- 

 • mitted many persons to train and qualify themselves for many 

 pursuits which do not contribute to the food-supply. The exist- 

 ence, among the hydroids, of a mechanism for feeding them in- 

 dependently of their own efforts, has permitted the same sort of 

 specialization to grow up, and even to become more perfect in 

 some respects than it is among mankind. 



The welfare of any species requires that the individuals shall 

 be supplied with food, protected from accidents and enemies, and 

 enabled to reproduce the species, and while many parasitic ani- 

 mals, and the young of many others, are supplied with food 

 without exertion, the conditions of their life do not usually per- 

 mit much specialization, and this does not, as a rule, occur unless 

 the individuals of the species form communities. The social ants 

 and bees are divided into castes, and the existence of hydroid col- 

 onies, which are structurally united into compound organisms, 

 presents the conditions which are most favorable for specializa- 

 tion among the members of the community. We accordingly find 

 among them the most remarkable examples of division of labor, 

 accompanied by structural specialization or polymorphism. 



A young dysmorphosa colony consists of a creeping root, which 

 carries a number of hydras, all of them like a in the figure. They 

 are the eating and digesting members of the society. Each of 

 them has a long tubular body, almost completely filled by a ca- 

 pacious stomach, which opens to the exterior, at the free end of 



