PROCURING OBJECTS. 57 



moves along the dorsal vessel towards the head and down the sides of 

 the body, in cavities and not distinct vessels ; hence called diffused 

 circulation. Even in the lowest forms of animal life, in the Acalephae 

 Infusoria and Polypi, it has been asserted, that the circulation has been 

 observed ; but these observations may be considered as liable to fallacy, 

 on account of the prevalence of various kinds of ciliary currents in 

 the interior of many of these animals. The striking analogy which 

 these currents bear to those occurring in the stems of some plants, as 

 Chara and Caulinia, seems to bring them under another class of phe- 

 nomena, than those of the vascular circulation of the higher animals. 

 The most favourable subjects for viewing this diffused circulation, 

 are the larva of the ephemera the larva of the hydro philns the 

 water-flea (daphnia pulex.) 



The circulation in plants termed cyclosis, is a revolution of the 

 fluid contained in each cellule, and is distinct from those surrounding 

 it. It can be observed in all plants in which the circulating fluid 

 contains particles of a different refractive power or intensity, and the 

 cellules of sufficient size and transparency. Hence all lactescent 

 plants, or those having a milky juice, with the other conditions exhibit 

 this phenomenon. The following aquatic plants are generally trans- 

 parent enough to show the circulation in every part of them : Nitella 

 Hyalina, Nitella Translucens, Chara Vulgaris, and Caulinia Fragilis. In 

 the frog-bit, (Hydrocharis,) it is best seen in the stipula of the leaves 

 and the ends of the roots. In the spider-wort, (Trandescantia Vir- 

 ginica,) it is seen in the filaments surrounding the stamens of the 

 flower. In the common groundsel, (Senecio Vulgaris,) it is said to be 

 seen in the hairs surrounding the stalks and flowers. 



60. In the foregoing pages, it has been the intention of the com- 

 piler to give a clear detail of the practical use of the microscope, and 

 to explain its manipulation. As stated in the outset, this was the 

 chief intention of the work ; but it was found impossible to omit 

 some reference to the wondrous revelations of this instrument. This 

 sketch of the extent and variety of the discoveries effected by the 

 microscope, is, from the limits cf the work, necessarily a brief one. 

 The continued use of the microscope, and tlie researches of naturalists 

 into the infinitude of the organized creation, have been the means of 



