322 HYDROID^. Part IV. 



SECTION VII 



EUCOPE DIAPHANA AG. 



Proles hjdroidea. AiJvIi. — The habitat of this Hydroid is either below low- 

 water mark, or else in deep pools which are not left more than an hour or two 

 uncovered by the sea. It evidently needs all the advantages of the open ocean 

 in order to thrive, and we find it very difficult to keep it alive, unless the water 

 in the jar is made icy cold. It is most frequently attached to the fronds of 

 Laminaria, but may be found on other sea-weeds. Its true characteristics are very 

 much disguised iniless it has a broad surface like that of Laminaria to creep 

 over, when its stolons pursue nearly straight courses, giving off, occasionally, a 

 branch to the right or left (PL XXXIV. Fig. 9), and, at regular intervals, an 

 upright stem. A colony of such Hydroids resembles a long row of trees vanishing 

 in the distance. Fronds of Laminaria, thrown up from deej) water, frequently 

 bear the most perfect examples of this peculiar mode of branching. It is a 

 remarkable fact, that the upright stems lean toward the direction of the growth 

 of the stolon, so that between each upright stem and the stolon from which 

 it springs, there is an acute angle (PI. XXXIV. Fig. 9) of about sixty-five or 

 seventy degrees. The upright stem is not more strongly zigzag than that of Obelia 

 commissuralis, or related species, but by reason of the great thickening of the 

 horny sheath (PI. XXXIV. Fig. 5, e^) on alternate sides of the successive joints, 

 the appearance of a zigzag is produced, whereas the covu'se of the chymiferous 

 cavity of the hydrarium is only slightly sinuous. In dried sj^ecimens, the zigzag 

 appearance becomes exaggerated by the unequal contraction of the corneous tube. 

 Each intermode {Fig. 5, e^) is twice as long as its greatest breadth, and the point 

 of its greatest thickening is always in the same plane, and coiTCsponds to the 

 direction of the stolon. In this plane, also, the pedicels which bear the calycles 

 have a general trend, and, therefore, have a distichous arrangement, but lean a 

 little to either one or the other side of it, all having the same direction, in this 

 respect, on the same stem {Fig. 8) ; but whether the pedicels of every stem, of 

 any one stolon, all lean to the right or all to the left, Ave are not certain, although 

 it seems to be so. The lowest pedicel of eveiy stem, arising from any one stolon, 

 originates on the same side ; either all are on the side toward which the stems lean, 

 and, consequently, in the acute angle, or all are on the ojDposite side, and in the 

 obtuse angle. From the thickest side of an internode, the tube of the main stem 



