STRUCTURE OF THE CYSTIDE^. 31 



IV. The Cystidece. 



Concerning the functions of the apertures of the Cystidece there 

 has always been much doubt; and in fact, at the present moment, 

 the only point that can be regarded as established by positive 

 evidence is, that the apical opening was the passage through which 

 the vessels of the ambulacra issued from the visceral cavity. All 

 the grooves of the arms or pinnulae take their departure from it ; — 

 there are no other apertures so situated with respect to the brachial 

 furrows that they could have subserved this function, and therefore 

 the conclusion, that it was the ambulacra! orifice, seems as well 

 founded as could be desired. There is not the least proof, except 

 the remote analogies furnished by the Star-fishes and recent Crinoids, 

 that it was the mouth ; and in selecting a name, therefore, the safest 

 course is to be guided by some known character, rather than resort 

 to the unknown. 



The large opening in the side, called the mouth in this memoir, 

 has been usually described as a genital or ovarian aperture, a view 

 first entertained by the late Baron Leopold von Buch, and accepted 

 with more or less hesitation by most authors up to the present time. 

 The idea originated altogether in the supposition that the Cystidese 

 were armless, and consequently that the ovaries could not have been 

 situated outside of the body. The following is von Buch's descrip- 

 tion of the Cystideae : — 



" The Cystidece were natural bodies supported on a stem or pedicle, which was 

 attached to the ground ; their surface, more or less spherical, was coTcred by a great 

 number of polyhedral plates, accurately fitted to one another, and between these plates 

 were certain openings necessary for the performance of the animal functions ; but from 

 none of these did arms proceed resembling those of the Crinoidece. The animal was 

 completely without arms. 



" With regard to the openings on the surface, we find in all the Oystidese -.—Ist. That 

 the mouth was planted in the central part of the upper surface, generally in a movable 

 proboscis covered with minute plates. 2nd. That besides this mouth, and close to it, 

 there is generally, if not always, a small anal orifice penetrating the plates, but not 

 itself surrounded with any plates peculiar to it. M. That further towards the middle, 

 but almost invariably on the upper half of the body on which the mouth is placed, 

 there rises a round or oval aperture, not connected with the mouth, and often covered 

 by a five or six-sided pyramid, which seems to be composed of as many little valves. 

 This probably forms the ovarian orifice of the animal. 



"These openings, with the exception of the mouth, are not found to exist when arms 

 begin to be developed from the upper surface ; and we may easily understand this when 

 we remember that in the latter case the ovaries are carried out with the arms beyond 

 the rim of the cup-like body, so that a separate opening for them would be useless. In 

 all Cystideffi the presence of these ovarian orifices is however manifestly essential." — 

 Von Buch: Uber Cystideen, Berlin, 1845. Translated in the Journal of the Geological 

 Society, May, 1845. 



