FORMS OF THE TOLYPIDOMS. 437 



solid axis, but there is an evident tendency to its formation ; 

 the materials lying scattered in the form of spicula in the 

 soft gelatinous centre. 



The polypidoms of the Hydraform and Polyzoan zoophytes 

 are more diversified in their figures and more decidedly ar- 

 borescent. The latter are formed by an aggregation of dis- 

 tinct cells, united in general after the fashion of the quincunx, 

 and spread out into leaves or layers or compressed branches ; 

 or the cells being placed upon each other in pairs, or even 

 in a single line, they form neat confervoid tufts ; or lying 

 immersed without any very traceable pattern, the masses 

 resulting from their union are amorphous, or at least incon- 

 stant and irregular. The horny material of the Hydra tribe 

 is always formed into tubular sheaths encasing the living 

 flesh, jointed at intervals, sometimes of the same calibre 

 throughout, but more commonly dilated at intervals into 

 vases or cups, or cells, in which the proper body of the 

 polype is placed. The manner in which the sheath or tube 

 is divided and branched, is limited in diversity only by the 

 number of the species, which are among the most delicate 

 and interesting of all polypidoms, and pre-eminently imita- 

 tive of vegetable forms. These forms are of course altogether 

 independent of their animated tenants, — these " have been 

 specicfially appointed by Him to do what they have done, 

 and are still effectuating. They are mere instrumentalities 

 at His command. They know nothing of the results they 

 cause, nor mean to perform any of them, nor could of them- 

 selves co-operate with each other, nor produce any systema- 

 tical arrangement, or regulated or orderly effects. It is their 

 Master and Maker who organizes, governs, and guides them 

 to those movements and operations which they perform, and 

 from all others ; so that by His directing will they are made 

 to do what we see them effect, and that only because He 

 restrains and averts them from all else."''^ 



The formation of polypidoms has been the subject of con- 

 siderable discussion. The opinion of Ellis, as we have al- 

 ready seen, was, that they are the result solely of a transuda- 

 tion, or excretion of the constituent matters from the body of 



* Turner's Sac. Hist, of the World, Vol. ii. p. 71. 



