Page:The Book of the Aquarium and Water Cabinet.djvu/97

Rh scale and approach the confines of the kingdom of verdure. Here, then, life has its lowest if not least lovely forms; the individuals have less individuality, many of them live in groups and clusters, and increase in a semi-vegetative manner by gemmation, or the formation of bud-like germs, while others generate by spontaneous fissure, and break up into numerous forms, each of which rapidly acquires the form of the parent, and proceeds in the same way to increase its kind.

The are so named on account of the ray-like form generally observable in the structure of the creatures; in some the ray-like divisions give such a speciality to the structure as to distinguish them at once as members of this division; as in the star-fishes, for instance, in which the intestinal canal branches out from the body into the several rays which form the star, and in the anemones, in which the relation to the tribe is at first sight perceptible in the tentacles which surround the mouth, and which render it so exquisitely beautiful as a marine representative of a true flower.

But though the term Radiata is applied to an extensive division, in which the members have many characteristics in common with each other, the ray-like form is not equally distinguishable in all. In some tribes there is a tendency to associate into groups, in which each individual has a certain degree of connection with the rest, as in the infusoria common in our brooks, and indeed most of the polypes which thus live in community. The resemblance to vegetable forms is, however, common to a great portion of the Radiata, and those in which this