80 Dr Gairdnei's Analysis of 



None of these animals excite any currents when immersed in a 

 solution of coloured particles, nor do they possess any organs to 

 -which we can attribute this faculty. Their most appropriate 

 place is probably among the Entozoa ; although the structure 

 of the seminal animalcules has not been as yet fully made out. 



They may be distributed into two very natural classes ac- 

 cording to their internal structure ; those provided with several 

 internal cavities or stomachs — the Polygastrica ; and those pro- 

 vided with but a single stomach or alimentary cavity, and pos- 

 sessing peculiar lotatory organs surrounding the mouth — the 

 Rotatoria. The first class is much simpler in its structure than 

 the other. They possess no vascular or nervous systems. The 

 genus Euglena presents the combination (well worthy of the at- 

 tention of the observing naturalist) of an immediate spontaneous 

 division, with indications of eyes, and consequently of a nervous 

 system ; indeed the sense of taste, which they distinctly possess, 

 would lead us to expect these organs. The Polygastrica, as 

 they are the most imperfectly known, so they will probably 

 stand most in need of farther changes. Dr Ehrenberg has 

 classed them under two groups. In the first are arranged those 

 which, from their minuteness, are very difficult to observe, and 

 in which, although possessed of a distinct mouth and stomach, no 

 oral orifice or excretion of colouring matter has been observed. 

 It is not probable, however, that the same orifice performs the 

 function of anus as well as mouth. To them Dr Ehrenberg 

 has given the name of Anentera *. The second group which is 

 by far the largest, the Enterodela^ possess a distinct orifice for 

 the ejection of the excrementitial colouring matter ; its position, 

 as well as that of the mouth, and the arming of the latter, fur- 

 nish good systematic characters for the subordinate divisions. 



The class of Rotatoria is much more complicated in its struc- 

 ture than the former. They are even more highly organized 

 than the Entozoa of Rudolphi. They are, however, well dis- 

 tinguished from the Mollusca and Crustacea, with which they 

 agree in the possession of nerves and vessels, by the want of a 

 central organ for the propulsion of the circulating fluid. Most 

 of the genera possess eyes, which furnish very good characters 



• From the privative co and sjrrg^ev intestine in the sense of Aristotle. 



