136' MUSCULAR SYSTEM. 



distinct in higher classes. In the outer layer of this mus- 

 cular coat, the short interrupted and interlacing fibres have 

 a transverse direction, and those of the same kind forming 

 the inner layer have a longitudinal direction, and are generally 

 grouped to form four lengthened contractile bands ; the 

 longitudinal fibres compose distinct muscles, especially at 

 the anterior part of the body where they are attached 

 to the moveable parts of the mouth. The muscular fibres 

 are not perceptible and the irritability is most feeble in 

 the cystoid and cestoid forms of this class. The long 

 pliant organs of attachment by which the entomoid forms 

 of these entozoa adhere to the surface of aquatic animals, 

 present generally distinct longitudinal muscular bands, as we 

 see in lern&a, and they are also developed for the movement 

 of the maxillae and other dense, and articulated parts of 

 their body. 



The muscular apparatus is most distinct and complicated 

 in most of the rotiferous or wheel animalcules, and cor- 

 responds with the high development of their nervous and 

 other important sytems. There are numerous fasciculi at 

 the anterior part of the body, for the movement of the long 

 vibratile cilia which surround the mouth ; the maxillae are 

 enveloped and moved by a strong muscular apparatus, which 

 can be deeply retracted within the body by longitudinal 

 bands, and similar longitudinal bands extend along the 

 whole internal parietes of their body for the retraction 

 and bending movements of the trunk. The muscles of 

 these animals, though most distinct, are almost as colourless 

 and transparent as the crystalline parietes of their body. 

 They are carried through the water by a slow and gliding 

 movement, produced by the rapid vibration of the long cilia 

 which surround the anterior parts of their body, and these 

 cilia while in action, appear like a revolving wheel from their 

 forward, slower and more forcible movement being alone 

 perceptible by the eye. The currents of water and the 

 surrounding particles move in the same direction in which 

 the circles appear to revolve. 



In the cirrhopods we find united in the same animals, 

 both the articulated and the molluscous forms of the mus- 

 cular system, and these are accompanied with a fixed con- 

 dition of the exterior shell, and a high activity of the enclosed 



