OR OSSEOUS SYSTEM. 13 



As in most other classes of invertebrata, we find many 

 zoophytes which are destitute of an external or internal 

 skeleton, as the common fresh water polype, or hydra. Be- 

 sides the solid internal skeleton in the corticiferous zoophytes 

 we commonly find in the fleshy crust itself minute calcareous 

 spicula. These small spicula compose the hard crust which 

 is seen covering the horny axis of the gorgonia, as it is com- 

 monly preserved dried in cabinets ; and in their occurring thus 

 spread through the general fleshy mass in gorgonue, lobularia, 

 and many other zoophytes we observe a lingering analogy 

 with the spicular form of the skeleton in the class of pori- 

 pherous animals, especially in the calcareous group. The 

 skeleton in the keratophytes is exuded from the fleshy sub- 

 stance in a soft and semi-fluid state, and quickly hardens after its 

 separation from the living parts upon which it is moulded. 



As the skeletons of zoophytes are not permeated by vessels, 

 or organized as it is termed, their materials do not expand by 

 growth, but encrease in dimensions by the mechanical addi- 

 tion of new matter. Hence in the vaginiform keratophytes, as 

 plumularia and campanularice, we find the base or lower part 

 of the stem, which was formed in the younger state of the 

 animal, to be smaller than the upper part of the stem, which 

 was formed of larger dimensions when the animal, or the 

 contained fleshy substance, had encreased in bulk and de- 

 velopment. The large globular masses ofmeandrince, astr&ce, 

 and similar solid lithophytes encrease in bulk by the constant 

 addition of new superficial layers of calcareous matter upon 

 the same primitive plan by the polypherous fleshy covering 

 of the mass. From the origin, and the mode of growth of 

 these calcareous masses, it is obvious that when torn from 

 their primitive seat, they may re-attach themselves, or con- 

 tinue to grow, by the deposition or exudation of new matter, 

 as long as the secreting fleshy crust retains its vitality. 

 These extra-vascular skeletons appear to be very little modi- 

 fied by the contact of the living fleshy parts after they have 

 been once deposited in a soft state, portion by portion, and 

 fully consolidated by the hardening of the glutinous matter 

 in the keratophytes, or by the deposition of earthy matter 

 in the more solid lithophytes. 



It is by the contact of living membranes, in the form of 

 capillary vessels, containing fluids, that the decayed earthy 



