234 HYDROID^. Part IV. 



prolongation, but, in proportion to the diameter of the tubes they form, they may 

 be said to be fully equal in this respect. They anastomose so closely, and have 

 such small interstices occupied by the uniform layer, that, in reality, the latter 

 fills much the smaller part of the whole bulk of the stolonic portion of the colony. 

 At the edge of the colony, Avhere the anastomosing tubes, budding laterally [Fig. 5", 

 /), are progressing in growth, the uniform layer {d) is in preponderance, but only 

 here. The chymiferous network not only covers the horny spines {Fig. 6), but 

 also penetrates through their lateral apertures into the interior. This is not at all 

 a different feature, however, from that observed in the horizontal parts of the horny 

 layer, when it is young and forms as yet only a network of more or less ele- 

 vated ridges, into the meshes of which these chymiferous tubes dip. The only 

 difference is, that the latter is horizontal, whereas the spines are the same network 

 much more elevated, as if pushed up from below. (See wood-cut 35, p. 238.) 



This horny layer, already so frequently mentioned, varies according to age; 

 at first it originates in isolated spots {Fig. 5, e e), which gradually dilate, 

 horizontally, at the same time that they become elevated (/), till finally they 

 coalesce and form a network. With age, the interstices of this netAvork become 

 filled up below, so as to cover completely the rock or shell, upon which the colony 

 has settled, with a continuous layer. The upper side of this layer still retains 

 its network form, the meshes constituting the elevated ridges, Avhich give a dried 

 specimen that honeycomb appearance so often noticeable. At pretty regular inter- 

 vals, these ridges begin to be elevated, more than the rest of the network, and 

 appear as low, conical, rough papillae. When seen from above, these papillas 

 look like stellate excrescences on a retiform groundwork. As the papillte grow 

 higher, this stellate appearance becomes more conspicuous, and the rays of the star 

 more prominent, till we may see that each ray corresponds to a single one of 

 the several ridges which unite to form a papilla. Each of the ridges rises fre- 

 quently into spinules, and these serve to render it bristling, and, when seen from 

 above, give the arms of the star a more slender appearance. With increasing 

 age, the papillse grow higher and proportionally more slender, and frequently curved. 

 In the latter stages of growth, they may more properly- be described as spinous 

 than papillate, especially the oldest ones, Avhich are quite slender and pointed. 

 We have already mentioned (p. 233) that there is no horny covering to the 

 upper side of the stolonic layer, nor to the hydroids which arise from it ; the 

 whole horny mass is a foot secretion, just as truly as it is among the Gorgonioid 

 Polyps.^ 



' See Dana, on the foot secretions of Gorgo- States Exploring Expedition, p. 54, § 49. Pliila- 

 niaj, in liis work on the Zoophytes of the United delphia, 1846, 4to. 



