Zoological Society, 67 



as thev are met with in examining the growing extremity and pro- 

 ceeding from it towards the mature structure, as long as the elements 

 are susceptible of isolation and individual examination. The anatomy 

 of the soldering particles, and their relation to the production of the 

 cavitary structure of the tooth, is specially dwelt upon. The solder- 

 ing particles are supposed to be isolated at first, but as they enlarge 

 they become connected by a thin film from their upper and under 

 faces. This occurs before the final consolidation of the tissue, and 

 before the soldering particles are indissolubly connected with, and 

 themselves indissolubly connect, the contiguous elements of the tooth. 

 At this stage these particles arestdl susceptible of isolation, and they 

 may be separated en masse, being held in relative position by the 

 films that connect them. The soldering particles and the connecting 

 films thus constitute a tubular system, which has an independent 

 existence before the final consolidation of the tissue ; and this tubular 

 system is introduced between, and interpolated among the previously 

 existing elementary parts of the tooth. 



The author concludes by expressing a coincidence of opinion with 

 Dr. Carpenter, that the minute structure of the tooth is essentially of 

 the same nature as that of the shell of the Echinidse generally. 



ZOOLOGICAL SOCIETY. 



February 12, 1861.— John Gould, Esq., F.R.S., V.P.,in the Chair. 



Observations ox the Anatomy of the Echinoderms. By 

 Thomas Howard Stewart, M.R.C.S., F.Z.S. 



There are certain points connected with the anatomy of the 

 Echinoderms which I am anxious to lay before the Society ; and the 

 more especially do I desire to do so, as I am not able to find any 

 true and accurate description existing of the very wonderful appara- 

 tus for the prehension and division of food, which some of the higher 

 groups of this class possess. I mean higher groups with regard to the 

 class itself. The animals forming this class, from their organization, 

 are placed low in the scale of creation, being just above the Polypifera 

 and below the Annelida ; yet we shall find, in the order Echinoidea 

 of this class, animals possessing what may be called a splanchnic 

 or oral skeleton, of so complicated and yet so eflacient an arrange- 

 ment, as cannot fail to make us wonder at the object of its sudden 

 appearance in the anatomy of animals ; nor can we help admiring 

 the beauty, and wondering at the perfection of the work. Those 

 who have not searched into the anatomy of these lower forms of life 

 might be surprised to be told that a creature just above the common 

 Sea-anemone, with an almost invisible nervous system, and other- 

 wise very low organization, possesses jaws (or, as I prefer to call the 

 apparatus, a splanchnic skeleton) of a more complicated arrange- 

 ment than any other animal in existence, from a simple sponge or 

 Amoeba up to man himself. This splanchnic skeleton, in Cidaris, 

 Echinus, and allied genera, is formed of forty separate calcareous 

 portions, arranged in a conical form, and, as we shall see by de- 



5* 



