Chap. I. STRUCTURAL FEATURES. 167 



lected by earlier observers is not surprising ; but that Gegenl^aur should have 

 published a figure and description of a new Cydippe, without noticing the 

 course of these tubes and the connection of the tentacles with this system, is 

 impardonable, the more so since he jDOsitively affirms that that species, Cydippe 

 hormiphora, has not only a hollow tentacle, but that the peculiar cirrlii attached 

 to it are also hollow, and communicate with the cavity of the tentacle. If these 

 tentacles were truly hollow, it would be of the highest interest to know in what 

 way the interambulacral tulles penetrate into their cavity, and what are the 

 relations of the currents extending into these tubes to the general circulation of 

 the ch3-miferous fluid through the whole system ; since in Pleurobrachia the inter- 

 ambulacral tubes do not extend beyond the base of the tentacular apparatus, and 

 the tentacles are not hollow. It may be that there are two types in the structure 

 of these interambulacral or tentacular tubes, as there are two types of tentacles 

 among the naked-eyed Medusae, some being hollow, as in Sarsia, and others plain, 

 as in Bougainvillea ; but, until the connection of the tentacular cavity of Cydippe 

 hormiphora with the interambulacral tubes, and the connection of these with the 

 central cavity of the chjaniferous system, be more fully ascertained, the statement 

 of Gegenbaur i-emains inisatisfactory. That a current through the tentacles is not 

 a necessary condition of their extraordinary jjower of extension and rapid con- 

 traction, is plainly seen by the fact, that the tentacles of Sarsia, which are hollow, 

 are neither more active, nor, comparatively to their size, more extensively movaljle, 

 than those of Bougainvillea, which are full. Milne-Edwards has mistaken the 

 bulb of the teutacidar apparatus of LeSueuria for a secretory organ, and erroneously 

 considered it as discharging its contents outward. It is certainly closed, and 

 no more open than the interaml)ulacral dilatations of the radiating tubes of 

 Aurelia, which Ehrenberg also erroneously described as opening outward, and per- 

 forming the functions of multiple anal apertures. I have carefully examined these 

 swellings in Bolina, LeSueuria, and Aurelia, and am certain, that, unless they are 

 accidentally injured, they in no way communicate with the surrounding medium. 

 That these tentacular tubes are interambiUacral, and not ambulacral, is at once 

 settled by their position, since they are intermediate between the radiating tubes 

 extending to and communicating Avith the vertical, peripheric, ambulacral tubes ; 

 but they are homologous to the simple radiating tubes arising in Aurelia from 

 the angles of the sexual cavity, and enlarging in the margin into the little pouches 

 mistaken by Ehrenberg for cloacas, and supposed by him to open outward through 

 as many anal apertures as there are such interambulacral radiating tulx's. The 

 tentacles connected with these tubes are therefore also interamlnilacral, and on 

 that account cannot be considered as homologous to the simple ambulacral tenta- 

 cles of Sarsia, or to the bunches of tentacles of Bougainvillea. We shall see 



