328 HYDROIDiE. Paet IV. 



of its depth it is attached, while the remaining third is free, and bent outwardly. 

 In this way, the whole series of calycles is arranged along the stem, from base 

 to apex, at such regular distances, that the base of any one is about double the 

 depth of a calyx from the base of the next one above or below it. At the 

 base of each calycle, there is an annular projection from its interior face, which 

 forms a diaphragmic semi-partition {Fiys. 2, d, and 12, c, d), through which the 

 hydra {Fig. 2, a, h) connects with the main stem of the hydrarium, but without 

 any, or with very slight constriction ; but the lateral portion of the calycle is 

 entirely closed up ; in fact, as we shall show hereafter, when describing its growth, 

 it has one and the same wall Avith the stem {Fig. 15, m), or rather the walls 

 of the two are soldered together. The general outline of the hydra-cells is 

 cylindrical, but not very regular, and the free, or actinal end, is more or less 

 curved outwardly, and slightly narrowed, so that the two opposite calycles, and the 

 included stem, form an equilateral, inverted triangle {Fig. 3). The aperture of the 

 cell is prolonged into two broadly triangular lips {Figs. 2, m, and 14, m), one on 

 each side of the plane through the two opposite cells, as if the cylinder had been 

 sliced obliquely across from two opposite directions, one cut facing toward the main 

 stem, and the other, the broader one, facing outwardly, and slightly to that side 

 toward which the cells converge. The base of a branch {Fig. 3, i) arises just 

 below the semi-partition of a hydra, and trends in a direct line with the plane 

 of opposite calycles, and, as we have mentioned above, the opposite calycles {Ic) 

 of a branch, or of a branchlet, always stand at right angles to these, on the stem 

 from which the branch arises. 



Tlie reproductive calycles {Figs. 7, 8, D, 10, and 10") are oval in outline, and 

 terminate with a slightly flaring, truncate aj^erture {g), wdiile below they taper 

 away into a pedicel {c), which is a little smaller than the main stem, and more 

 or less curved in the same direction, toward Avhich the sterile calycles converge. 

 Oftentimes we meet with a reproductive calycle, taking, as it were, the place of 

 a branch, the latter being present on the opposite side ; but most frequently they 

 occupy both sides, or one side is destitute of any lateral growth. Occasionally 

 we find two or three reproductive calycles {Fig. 10"), arising from one joint. 



The soft part of the hydrarium, or the hydra proper, is double-walled throughout 

 {Figs. 2, a, b, 12, a, h, 8, 9, and 10, a^ e) ; the stolonic part is a uniform, smooth 

 cylinder ; in the upright stems it arises directly, and at right angles, from the 

 stolon, and proceeds with uniform thickness to a point just below the calycles, 

 where it expands upon two opposite sides, and gives oflf from each a single uniform 

 tubule {Fig. 2, c, c'), which, passing through the diaphragmic semi-partition {d), 

 traverses the calycle, and terminates in a simple, short, conical proboscis {p), around 

 which a single row of slender, tapering tentacles, usually sixteen in number {t), 



