6 



Many Physiologists consider that each polype of a poly- 

 dom, is a distinct being, and consequently that each polypidom 

 is a congeries of animals united by a common axis. Though 

 it is not of much importance whether we deem this opinion 

 right or not, yet it will be best to consider the whole as one 

 compound being, and the polypes as so many mouths through 

 which the nutrition is taken in. There is nothing more 

 visionary in this multiplication of mouths, than in the multi- 

 plication of feet in worms. The number of polypes on a 

 polypidom varies according to the species, age, luxuriance 

 and innumerable other circumstances; but sometimes the 

 number is so great as to fill the mind with astonishment, and 

 the wonder is increased the more we consider it. In a spe- 

 cimen of Sertularia argentea of luxuriant growth, in my 

 possession, eighteen inches high, there are five pinnss in a 

 whorl, about fourteen whirls in an inch, and about thirty 

 cells on each pinna, making the polypidom to contain the 

 enormous number of 37800 individual polypes in the space of 

 a foot and half. 



There is but little community of feeling existing between 

 the different polypes of the polypidom; nor can it, I think, 

 he expected from the nature of their internal structure. 

 No nervous system has yet been discovered, and from the 

 simplicity of their organization, no such discovery, is likely 

 to take place. An impression to be felt by more than 

 one polype, must be somewhat roughly communicated, since 

 it is probable, that impressions are communicated chiefly by 

 the contact of the granules. 



It is generally allowed, however, that there is a community 

 of nourishment, and no one, who has watched these animals, 

 will call it in question. If a Sertularia be taken, and one 

 only of its polypes be fed, nourishment is evidently supplied 

 to all the rest and to the central pulp, which according to 

 Grant * is furnished with a central canal, through which 

 the nutrient matter is conveyed. The tentacula like the 

 body, are contractile in every part, and are tuberculated ; the 

 tubercles being circularly arranged. Grant is evidently in 

 error when he says that the tentacula are ciliated, for after 

 many microscopic examinations on the majority of the Cornish 

 species, I have never detected cilia in a single instance, and 

 Dr. Johnston, a good authority, is of the same opinion. The 

 mouth is also capable of a great deal of elongation and con- 

 traction, sometimes being conoidal and at others flat; so that 

 at different times the polypes present a great diversity of form. 



* Outlines of Comp. Anat., p. 13. 



