of the Chalk. 191 



of different members of the highest orders of recent zoophytes 

 with the addition of other and very important characters present 

 in none of the latter. And those characters are peculiarly in- 

 teresting as leading perhaps to some settlement of the long-moot 

 question both as to the nature and mode of growth of polypi - 

 doms*. Let the beautiful and delicate tissue of the central po- 

 lypidom — its entire separation and distinctness both from the 

 substance and structure of the root — its investing under-skin still 

 again differing in structure — be considered, and it must be per- 

 fectly obvious that the polypidom of the Ventriculidse was no 

 transudation or excretion from the body of the polyps ; and it 

 will surely be no less evident that it owed its origin to no mere 

 vegetative principle. In addition to the peculiar character and 

 beautifully regular structure of the whole mass, pervaded as it is 

 with one aspect of admirable unity f, let the special adaptations 

 of each part, as already pointed out, to subserve the ends of the 

 preservation and safety of the whole and of each individual polyp 

 be considered ; and can the conclusion be resisted, that the entire 

 creature, the whole polypidom with its whole array of polyps, 

 formed one peculiar and highly organized animal, many-headed 

 or rather with many separate special organs of nutrition un- 

 doubtedly, but still a unity, an entire animal, of which the poly- 

 pidom was one constituent and essential part, which can no more 

 be properly considered without reference to its polyps, or its 

 polyps without reference to it, than can the bones of a mammal 

 be considered without reference to its soft parts, or the soft parts 

 without reference to the bones ? 



* An apparent inconsistency is found on this point in Dr. Johnston's 

 valuable work, the Asteroida being described in terms exactly opposite on 

 pp. 140 and 255. 



f In all the observations as to the unity and entirety of the polypiferous 

 mass, the whole groups of Eschara, Flustra, &c. are necessarily included. 

 It may be matter of discussion whether the individual polyps of these are not 

 separately true Ascidians. There can be no question, at any rate, that it is 

 a part of the necessity of their nature to exist always grouped thus, and in- 

 separably united by an organized medium. That organized medium is 

 clearly therefore necessary for the safety and security and existence of each 

 polyp; and whether we look at the mass of an Eschara foliacea or of a 

 V. simplex, the argument is the same. That organized medium being thus 

 necessary for the safety, security, and existence of each individual polyp, or, 

 if you please, Ascidian, the more perfect the provision in it for that indivi- 

 dual safety and security — and therefore for the fulfilment of the ends of the 

 individual existence — the higher must be the rank of the creature, whether 

 looked at as one entirety or as an aggregation of individuals. What those 

 provisions are in the Ventriculidae has been seen. The octahedral structure 

 is a special and elsewhere unapproached provision for the security of the 

 individual polyps (or Ascidians). 



[To be continued.] 



