ANIMAL ORGANIZATION. i)\ 



locks of a canal.* Among the numberless instances 

 of express contrivance which are met with in the 

 examination of the fabric of animals, there is per- 

 haps none more striking and more palpable, than 

 this admirable mechanism of the valves. 



As we ascend from the simpler to the more com- 

 plicated systems of organization, adapted to a 

 greater range of faculties, we find greater diversity 

 in the mechanical means employed for carrying on 

 the functions of life. Textures of greater strength 

 than can be constructed by membranes alone be- 

 come necessary for the security, the support, and 

 the defence of important organs ; and more espe- 

 cially for the execution of extensive movements. 

 For obtaining these advantages a peculiar species 

 of fibres is provided, formed of a much denser sub- 

 stance than even the most consolidated forms of 

 cellidar texture. The animal product termed albii- 

 men possesses a much stronger cohesive power than 

 gelatin, which is the basis of membrane. The 

 addition of albumen, therefore, procures the quality 

 required : and the fibres which are produced by 

 its combination with gelatin are opaque, and of a 

 glistening white colour. By interlacing fibres 

 thus composed, a close texture is formed, which is 

 exceedingly tough and unyielding. These fibrous 

 textures, as tliey are termed, while they retain the 

 flexibility of membranes, greatly surpass them in 

 strength ; but, being at the same time incapable of 



■ * Fig. 27, representing the section of a vessel, is intended to 

 show the position of the valves when applied to the sides of the 

 vessel, by the stream moving onwards in the direction pointed out 

 by the arrow. In Fig. 28, they are seen closing the passage by the 

 pressure of the retrograde current. 



