MUSCULAR SYSTEM. 131 



The action of vibratile cilia is always so much independent 

 of the will, or connection with the rest of the body, that it 

 continues for some time after the part to which they are 

 attached has been severed from the animal ; and this is 

 observed even in those of adult birds and quadrupeds. Jaws 

 containing sixteen teeth have been detected in the loxodes 

 cuculluluSy which necessitate great muscular development in 

 this minute polygastric animalcule. 



The soft cellular tissue which pervades the whole fibrous 

 texture of poripherous animals, and lines their pores, canals, 

 and vents, does not exhibit distinct signs of irritability or 

 contractility when acted on by the strongest stimulants, and 

 the currents continue to be impelled rapidly through these 

 passages even in thin portions cut from the body. It is 

 probable, therefore, that the currents are produced solely by 

 means of cilia which are numerous and large over the sur- 

 face of these animals, when in the state of gemmules newly 

 detached from the parent. The ciliated free gemmules of 

 poriphera do not exhibit signs of irritability by contracting 

 their body, and changing their form like those of zoophytes. 

 The cellular substance of the poripherous animals, being 

 still of a soft and semi-fluid consistence, is incapable of 

 effecting any perceptible movements in the fibrous skeleton 

 which it permeates. The general fleshy mass of the body 

 possesses distinct though languid irritability in almost all 

 forms of zoophytes, although the fibrous structure is seldom 

 developed in any part. This property is manifested in the 

 lobidaria by the spontaneous slow contraction and dilation 

 of its body at different periods of the day by the influence 

 of temperature and light, or by the slow contraction of a 

 part of the body which has been touched or irritated. This 

 fleshy contractile part is the same which secretes the solid 

 matter of the skeleton in this class, and developes the po- 

 lypi from different parts of its surface. The relation of this 

 irritable and secreting part to the internal axis in the corti- 

 ciferous zoophytes is seen in the section of the isis hippuris, 

 (Fig. 62. B.) where the calcareous solid portions (#,) and the 

 flexible, elastic, ligamentous parts (b,) occupy the centre of 

 the fleshy substance (c,) and the cells of the polypi (d, d 9 ) 

 are seen to be here confined entirely to this irritable crust, 

 and to leave no impression on the axis. The polypi are the 



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