LU CERN A RI.E AND THEIR ALLIES. Go 



what they receive to other regions, with no more special adaptation for doing so 

 than at any chance place. 



130. Nei-vous Centres. — We are not willing, however, to accept this conclusion 

 in its fullest sense, for we are too well aware of, and have said not a little in regard 

 to, the relation of tlie nervous mass to the polar regions of the typical animal. 

 Whatever the apparent diffuseness of the nervous centres may be, there can be no 

 misapi)rehension as to their tendencies toward concentration in a certain region of 

 the body. Any motion having a determinate end must be under the control of an 

 influence which emanates from a well-defined site, to which all others, however 

 diffuse, must stand in the relation of accessories, outlying posts, or frontier sentinels. 

 The fact that all eggs, not excepting those of the lowest animals, exhibit a 2>oh(riii/, 

 conjoined with the equally important fact that, at least in the middle and liighest 

 classes, these poles correspond respectively to the nervous and nutritive regions of 

 the body, giving one tlie highest warrant for the assumption that even in the most 

 inferior ranks there is a slight preponderance of the nervous elements, a tendency 

 to centralize, in some one region rather than in another. The line of separation 

 may be no more trenchant than that between the albuminous and oleaginous poles 

 of the egg, and yet it will be enough to indicate an oppositeness of condition. 

 And so we conclude, then, that, although tlie Lucernariae have no visible nervous 

 system, there is at least one or more regions of centralized power, from which 

 nervous currents emanate and in which sensation leaves its impress. 



131. Uomological Position. — We cannot dismiss this subject without drawing 

 particular attention to the liomological position of the eye-spots, and thence to 

 their significance as indicators of a specialization of tlie nervous system in reference 

 to their function. They stand respectively, four opposite the flanks of the pro- 

 boscis, and four opposite the angles of that organ. They are also subterminal, i. e., 

 not at the distal end of the tentacle (anchor), but at its base, or, more properly, 

 where the base joins the umbella. By their swollen, boss-like character they 

 remind one of incipient tentacles, springing up close to the next older that preceded 

 them. They are then probably to be set down as rudimentary oculiferous tentacles 

 situated within the line along which the anchors are disposed. Now in all 

 Acalephae the eye, so called, stands in close proximity to the margin of the umbella, 

 and always in connection with its circunioral parictes. The Charybdeida? are not 

 e^en an exception to this, nor the yEginida? ; notwithstanding the ocular peduncle 

 projects from the aboral side, its base is attached to the circumoral face. Rarely 

 it lies on the distal side of the base of the tentacles, as in the medusoid of Coryne, 

 but most frequently on the proximal side, as in Bougainvillia, Eucopidae, etc. In 

 the highest of the Hydroida (Tiaropsis, and the like), it is totally disjoined from 

 the tentacles, but still is within, and not on, the line along which the latter are 

 arranged. In the Strobiloida — v/hose optical apparatus is far more highly developed 

 than in Tiaropsis and others of the superior ranks of Hydroida — the eye is borne 

 on the end of a cylindrical, tentacle-like peduncle, and yet it is never marginal, 

 but submarginal. It lies in a different line from the tentacles, whether the latter 

 be strictly marginal, as in Aurelia, or submarginal, as in Cyanea. All of these 

 correspondences form the thread which guides one from the lower depths of ocular 



9 May, 1877. 



