180 DESCEiPTlON OF [Pol^/ffastricu. 



am2)lifying power of 400 diameters, is required ; but even a single 

 lens of that power will shew it. 



I may remark here that many observers with the microscope, and 

 even acute naturalists, have been unable to see the circulation in 

 these creatures, and I have for many years past received queries on 

 this subject ; even Mr. Ralfs, in his beautiful work on British Desmi- 

 diece, had not seen it until shewn by Mr. Brawerbank. This is 

 the more remarkable, as a good single equi convex lens ■will exhibit 

 it. The difficulty appears to me to arise from the want of proper 

 adjustment of the focus. The best method is carefully to adjust the 

 focus of the microscope for a distinct vision of the outer shell, then to 

 bring the object a little within the focus and the circulation, will be 

 seen ; the vision of the shell being indistinct. For observations on 

 the cii'culation, stops or diaphi'agms, under the stage, may often be em- 

 ployed with advantage ; a large angle of apertui-e not being essential. 

 The circulation in the Closterina resembles the diffused circulation in the 

 aquatic lavae of insects, or that seen at the joints of the legs of spiders . 



This phenomenon is sometimes compared with the cyclosis in the 

 Char a and other plants. 



Elu'enberg gives the following reasons for placing the Closterina in 

 the animal kingdom : — First, they exert a voluntary motion, as 

 shewn fii-st by Corti. Secondly, they have apertures at their extre- 

 mities, as noticed by himself. Thirdly, they have projecting organs 

 near these apertures, perpetually in motion. Foui'thly, they increase 

 and multiply by a transverse self-division, as observed by Miiller. 

 These four endowments Ehrenberg considers as being abundantly 

 sufficient to detennine the real nature of the Closterina, inasmuch as 

 whereevcr voluntaiy motion, an aperture or mouth (feet), and spon- 

 taneous division exist, you may conclude at once, ivithout ivaiting to 

 Me the creature eat, that the supposed plant is indeed an animal. 



Since the above was written, some interesting obsen'ations have 

 appeared in !N^o. xxxiii. of the Annals of Natural History, by Mr. 

 Dakymple, from which I select the following ; my intention in this 

 work being not to confine it to my own views, but also to record 

 those of others, belics-ing that, by so doing, I shall best serve the 

 public, and advance this science. 



Mi'. D. describes the Closteriiim as consisting of " a green gelatinous 



