232 HYDROID^. Part IV. 



frequently seen coiled upon themselves, in one, two, three, or fourfold spirals (wood- 

 cut 33, p. 228, d c f g h). Here, too, they reach their extreme height, one 

 quarter of an inch or more, in many cases, especially in the branching individuals 

 (wood-cut 33, e (j, p. 228). Excepting in their great length, they are indentical 

 with those which are full of medusaj-buds ; the smaller heads of the latter being 

 perfect counterparts, as to the proboscis, mouth, and tentacles, of tlie former. The 

 fact that they do not bear medusas, so far as we have been able to ascertain, 

 does not prove, by any means, that they are forms of a truly definite nature, 

 inasmuch as we find, everywhere throughout the colonj^, many of the reproductive 

 hydroids totally destitute of buds, whilst the others are full of their broods.^ 



The sterile Hydroid. — Below the head there is no difference in the internal 

 structure of the body of the sterile Hydroid, either in the male or female colonies, 

 from that of the reproductive form, nor does their shape vary from that of the 

 latter. The head, however, has a very different appearance, and even those of 

 the male and female colonies are unlike, as we have already pointed out. A 

 sterile Hydroid of either a male {Fhj. 2) or female colony {Fi(j. 1), has long, 

 slender, tapering tentacles {Figs. 2, H, and 1, D), disposed in a single row, like those 

 of Tubularia or Campanularia. During the contractions and contortions of the 

 head, the tentacles are sometimes displaced and rearranged, more or less alternatingly, 

 in two rows {Fig. 2''), one of which (/) stands out in a more spreading manner 

 than the other (/^), the latter being bent upward toward the mouth (»«). How- 

 ever, this does not always happen ; on the contrary, the tentacles oftentimes remain 

 as distinctly in one row {Figs. 1", i, V, t, and 2^, i) as when fully stretched out. 

 The base of each tentacle appears to be decurrent on the stem {Fig. 1, I), under 

 certain conditions, and, on this account, it is oftentimes difficult to determine their 

 exact relation to one another, and to ascertain whether a tentacle is above or 

 below the one next to it, on each side. 



When the tentacles are fully expanded, these difficulties are not in the Avay, 

 and there can then be no doubt that they are truly uniserial in their arrangement. 

 Unless luider very favorable circumstances, the hydroids do not fully expand their 

 tentacles in confinement, but keep them more or less contracted, in various shapes, 

 either club-shaped at the ends {Figs. 2, D E F G I, and 2'', t i^)^ or broadly 



' Dr. T. Strethill AVriglit lias published an arti- form of individuals, and still less as organs, as he 



cle in the Edinburgh New Philosophical Journal regards them, we think will be sufficiently clear 



for April, 1857, on Hydractinia echinata, in which upon reading the results of our observations upon 



he, for the first time, has brought these peculiar a species hardly distinct from that of Europe, 



modifications of the fertile hydroid into notice, ^ Hassal, in the Annals and Magazine of Nat- 



under the name of "Ophidian, or Spiral Polyps." uial History, Vol. VII. p. 371, Jul^s 1841, under 



That they ought not to be considered as a distinct the name of Ecliinocoriura clavigerum, describes 



