Chap. VII. DYNAMENA PUMILA. 



327 



and the origin of the upright stems, which bear the hydrc^, may be readily traced; 

 but when these animals grow upon the narrow branches of the more slender 

 Fucoids, the stolons cross and recross each other, in such an inextricable mass, 

 that it is next to impossible to distinguish one hydrarium from another. The 

 creeping stolonic stem has the appearance of being more slender than the upright 

 stems, but in reality it is quite as thick as the latter, which only seems more 

 stout, because it is bordered on two opposite sides by the calycles of the hydrse. 

 The upright stems vary in height, from half an inch to an inch and a half, 

 according to the position in which they grow; those nearest low-water mark being 

 usually the most luxuriant, and more or less branching, while those at higher 

 levels are quite simple, as our figure represents them {Fig. 1). Some specimens 

 in my possession are an inch and a half high, and tripinnately branched, but by 

 far the greater number of those collected between high and low-water are, at 

 most, an inch high, and branch only once. The stolonic portion of the colony 

 IS about as thick as common sewing-thread, and clings very closely to the surface 

 upon which it creeps. At irregular intervals, varying from one twelfth to one 

 sixth of an inch, the upright stems arise from the stolon, and in such a way 

 that the opposite cells {Fig. 3, op, op) of the hydr£e stand transversely to its trend. 

 The upright stem is straight; it has, at least, no abrupt turns, but may be, as 

 a whole, gently curved from base to tip. At pretty regular intervals, usually 

 equal to the breadth of the stem, the calycles {Fig. 2, 3, 6% 12) stand in pairs 

 above one another; they are not exactly opposite, but converge slightly toward 

 one side of the stem, and that side faces toward the younger part of the colony; 

 the same is the case with the branches, the calycles of which, standing transverse 

 to those on the stem, converge toward the upper side. This is carried out with 

 the most perfect regularity, even to the second and third branching, and, moreover, 

 the reproductive calycles, which, like the branching ones, usually arise from, or just 

 below, the bases of the sterile calycles {Fig. KP, A), all converge in the same 

 direction as the latter. The first, or lowest pair of calycles, is situated about 

 the depth of a cell from the base of the stem; the latter rises with a slight 

 constriction, and then expanding, transversely to the trend of the stolon, into" a 

 V-shaped form {Fig. 6»), suddenly contracts to its former breadth, and then proceeds, 

 with a slight and gradual widening, a short distance, varying from one half to 

 twice the distance across the V-shaped portion, and finally contracts to the same 

 thickness which it has at the base. On that side toward which the calycles 

 converge, the stem, which lies between them {Fig. 2), appears quite narrow, when 

 compared with the other side {Fig. 12) from which the calycles diverge. Upon 

 each of the two arms of the V, and against the gradually widening portion rising 

 immediately above it, a calycle is placed in such a manner that for about two third" 



