EESPECTING VITAL MOTION. 5 



and it is relaxed or expanded in summer. When 

 exposed to cold, also, the dartos contracts in a very 

 remarkable manner, and an opposite condition is 

 induced by the operation of warmth. And so likewise 

 in the vascular coats of erectile tissue. 



These instances furnish different points of view, 

 from which we may regard all the principal forms of 

 rudimentary tissue. The irritable tumours of the 

 sensitive plant consist chiefly of cells which do not 

 differ from the ordinary cells of plants. Areolar 

 tissue is composed of fibrils of various sizes, which are 

 formed from the same material as the primary cells, 

 and which material appears to be absolutely identical 

 in plant and animal. The tunic of the dartos is 

 only another form of areolar web, in which there is 

 a preponderance of certain thicker fibres, that are 

 present everywhere in less abundance; and between 

 these fibres and those which enter into the composition 

 of the vascular coats, there is a direct and immediate 

 gradation. Each form, indged, is transitional to the 

 other, and the whole constitute a group that includes 

 all structures subordinate to true muscle. It is of 

 moment, therefore, that we find these tissues to con- 

 tract when exposed to cold, and to pass into an oppo- 

 site state under the influence of warmth, inasmuch as 

 this action must be supposed to be common to all the 

 rudimentary tissues of the economy. In this way, 



