60 



LUCERNARI^ AND THEIR ALLIES. 



perhaps higlicr form, the blood going to the respiratory surfaces in distinct tubes, 

 after the manner of the Vertebrata. Again, anil finally, there are tlie Cystideans, 

 pn)totyi)esof the llolothuria Apoda, and, if we mistake not, the genuine progenitors 

 of llolothuria, exhibiting, like the highest of the latter, the clearest bilaterality and 

 a strong reduction or suppression of the dorso-ventral repetition of parts. Their 

 sedentary condition and a certain want of regularity and definiteness in the arrange- 

 ment of their plates, are indicative of their iixferiority, at least in tlie latter respects, 

 to those Crinoids which have been disposed in systematic order. In our Lucernarian 

 there is very little left, in point of inferiority, that debars it from taking the highest 

 rank among Acalephfe. On a former occasion^ we have placed the Lucernariae — 

 in a tabular view of their systematic position — as if intermediate in rank between 

 the StegamplLihahnata and the Gyriinopldlialmata. We think now that it would 

 be doing better justice to arrange them almost on a level with the Steganoplithalmata, 

 overlapping their lower ranks, as it were, but failing to come up to the horizon of 

 the topmost grades. But we are anticipating what we shall present in regard to 

 this matter in another chapter (Part X), and we have yet in reserve more matter 

 of equal interest to those who are curious to know what the status of our Acalephan 

 subject may be. We have allowed ourselves to be diverted into this digression 

 merely for the sake of laying heavier stress upon the quality and value of the 

 singular diversities of differentiation in the digitull, while the mind is fresh from 

 the work of investigation. Let us, therefore, recapitulate their prominent features 

 in brief terms, and then proceed to the subject of the next section. In the first 

 place they are lanceolate and flat. That leads to a survey of their position, in 

 which we find their broad sides systematically facing toward and away from the 

 proboscis. Again, these broad sides are diverse in character, the diversity of one 

 kind always on the corresponding side: for instance, the one bearing the coUetocysts 

 facing toward the proboscis, and the other, covered by vibratile cilia and bearing 

 nematocysts, facing in the opposite direction. Then there is the muscular layer 

 more pointedly separated from the chondromyoplax than in the diijituU of Aurelia, 

 and doubtless others of the same order. And, finally, not only do the fibrill.TC wliich 

 traverse the chondromyoplax trend at right angles to those in the circumoral 

 parietes, but they stand in very exact relations to the form of the digituli, trending 

 directly from one broad face to the other, as if linking the layers of coUetocysts 

 and nematocysts to each other. 



§ 16. The Digestive System. 



\22. Forced EomoJognes.—'We have scarcely anything to do hero in the way of 

 a description of the digestive system, since nearly all that is concerned in it has 

 been so thoroughly delineated from another, or several points of view as to render 

 further illustration entirely superfluous. It will suffice, therefore, if we do no 

 more than enumerate the several regions of the body which take part in the 



' Lucernaria tbo Coonotype, etc., ut sup., p. 22. 



