The hydrorhiza as well as to the other Agassiz, Contributions to Nat.
The foot by which it is attached often sends out root-like processes - the hydrorhiza (c).
The gymnoblastic polyp usually has a distinct perisarc investing the hydrorhiza and the hydrocaulus, sometimes also the hydranth as far as the bases of the tentacles (Bimeria); but in such cases the perisarc forms a closely-fitting investment or cuticule on the hydranth, never a hydrotheca standing off from it, as in the next sub-order.
As a general rule polyp-buds are produced from the hydrorhiza and hydrocaulus, while medusa-buds are formed on the hydranth.
In massive colonies of this kind no sharp distinction can be drawn between hydrorhiza and hydro-, .
The perisarc when, present invests the hydrorhiza and hydrocaulus; it may stop short below the hydranth, or it may extend farther.
Common flesh, which cannot be assigned more to one individual than another, but consists of a more or less complicated network of tubes, corresponding to the hydrocaulus and hydrorhiza of the primitive independent polypindividual.
The planula may fix itself (I) by one end, and then becomes the hydrocaulus and hydranth, while the hydrorhiza grows out from the base; or (2) partly by one side and then gives rise to Modified from a plate by L.
In different parts of the coelenteron the endoderm may be of three principal types - (i) digestive endoderm, the primitive type, with cells of large size and considerably vacuolated, found in the hydranth; some of these cells may become special glandular cells, without flagella or contractile processes; (2) circulatory endoderm, without vacuoles and without basal contractile processes, found in the hydrorhiza and hydrocaulus; (3) supporting endoderm (fig.