238 



HYDROIDiE. 



Part IV. 



Fig. 35. 



beyond these the thread gradually tapers into a long, slender, naked filament (c) 

 which is ten or twelve times as long as the cell itself. 



The smaller lasso-cells {Fig. 10, a, h) are excessively minute, and appear like 

 mere threads (a) when observed by the side of the other kind {Fig. 11) under 

 the same magnifying power; they are too small, in fact, to be delineated except 



by a line ; — but as the eye can detect the form 

 which is too minute to be drawn in its Ucatural size, 

 an exaggerated drawing {Fig. 10, b) must be used for 

 illustration. When the lasso is out, the cell is pear- 

 shaped, and to its narrower end an excessively long, 

 naked thread {h) is attached. When the cell is closed, 

 it appears as a mere oblong speck. These lasso-cells 

 are most frequently seen upon the medusoids. 



The Hornij Basis. — We have already shown that 

 this layer is a foot secretion, but have not described 

 the manner in which it increases, and from being 

 a simple, slightly uneven layer, becomes a very brist- 

 ling coat of spines and anastomosing ridges. This 

 horny substance is so transparent, that there is not 

 the least difficulty in detecting its most intimate 

 structure, without the necessity of making sections. 

 At the thinnest portions of the layer (wood-cut .35, a) 

 only one, two, or three layers may be seen, but as 

 the projections grow higher, the layers become more numerous {b) ; in the large 

 spines (c) they are most numerous. We hardly need say that these facts clearly 

 point to a successive deposit of layers, by which the thickness of the horny mass 

 is increased. When seen superficially, the layers show no trace of structure, nothing 

 like fibres, but appear to be perfectly homogeneous. 



The Egg. — The yolk, from the earliest period, has a transparent, grayish aspect, 

 which becomes granulated, and, in consequence of this, denser and darker. (See 

 Fig. 3% y.) The oldest eggs we have seen have a rather coarsely granulated yolk 

 {Figs. 3", g), a large, clear, homogeneous, Purkinjean vesicle {p), a single, but less 

 transparent, Wagnerian vesicle {w), occupying more than one third of the diameter 

 of the Purkinjean vesicle, which is nearly filled by a very transparent, homogeneous, 

 Valentinian vesicle {vl). In all essential characters, the mode of development of 

 the egg and the phases through which it passes are the same as in Coryne 

 mirabilis. See p. 210 and PI. 18, Fig. 20 to 24. 



The Spermatic Particles. — The male medusoids (PI. 10, Fig. 2, A, B, C, e, Fig. 

 4% a-i, Fig. 4*", Fig. 9) may be always recognized by their homogeneous contents, 



Longitudinal section of a horn-like spine 

 of the stolonic basis of Hydractinia polyclina; 

 to show the concentric layers, the apertures 

 (dt/i), and the interior cavity (e). Magnified 

 200 diameters. Drawn from nature, by H. J. 

 Clark. 



ab processes from the horizontal layer. — c spin- 

 ules. — d apertures leading to the central cavi- 

 ty (*)■ — ^ hole through the horizontal layer. — 

 / the shell to which the hydrarium is attached. 



