348 THÉEL, SKELETON OF THE ECHINODERMS. 



and their ends finally become combined by a membranous ring^ 

 the whole thus presenting a hollow mould, into which the cal- 

 careous salts are continuously carried in fluid form in order 

 there to solid i fy. 



Considering the authority of Chujst, there is no doubt 

 that the observations are right, but it remains to be learnt 

 whether be has made bis investigations on living materials or 

 not. In the former case this interpretation must be correct, 

 but in the latter the question ought to be left open. Supposing 

 the alcohol in which the objects are kept had been adulterated 

 by the smallest quantity of any acid, the result must have been 

 a gradual dissolution of the skeleton. I have often seen Holo- 

 thurids and larvae of Echinoids with their calcareous bodies in 

 all stages of dissolution, and then falsely one gets an impression 

 of these deposits being in diff'erent states of development. Pre- 

 suming this to be the case even with the Auricularia-wheels in 

 question — though it does not seeni probable — a conformity be- 

 tween the two extremes of developmental phenomena can be 

 traced. Expressly accentuating it to be nothing eise but a hy- 

 pothesis, I may be allowed to put forth the following interpre- 

 tation: l:st The «calciferous cell« may either be a true syncytiura 

 or Plasmodium ^) or an aggregation of close-lying cells with their 

 clear peripheral ectoplasm flowed together and mixed; 2:nd The 

 cell-merabrane should be the contour of the surrounding con- 

 nective tissue, and 3:rd The second membrane, which should 

 arise inside the former and by degrees assume the shape of the 

 hollow mould of the future wheel, should then be the decalcified 

 organic rest of the wheel with darker contours, a well known 

 sight in all Echinoderms treated with a dilute Solution of osmic, 

 chromic or other acids. Of course, the above attempt at an 

 interpretation does not lay elaim to consideration, except in case 

 Chun has founded his yiews solely on researches made on ani- 



^) In his paper Metsch^>iiroff describes such plaemodia in Phyllirhoé, Bi- 

 pinnaria etc, which attack and destroy such foreign particles as are too 

 voluminous to be absorbed by a single wander cell or phagocyte. 



