DESMIDACEJE. 411 



stance was granulated, and all the grains gave with iodine a beautiful 

 blue colour, as is the case with starch."* 



Did we trust solely to the eye, we should indeed be very liable to 

 pronounce these variable and beautiful forms to far more closely re- 

 semble animals than vegetables in their appearance. All favours this 

 supposition. Their symmetrical division into parts ; the exquisite disk- 

 form, finely cut and toothed Micrasterias ; the lobed Euastrum ; the 

 Cosmarium, glittering as it were with gems ; the Xanthidium, armed 

 with spines ; the scimitar-shaped Closterium, embellished with striae ; 

 the Desmidium, resembling a tape-worm ; and the strangely insect-like 

 Staurastrum, sometimes furnished with arms, as if for the purpose of 

 seizing its prey ; all these characteristics appear to a superficial ob- 

 server to belong rather to the lowest forms of animal, than vegetable 

 life. Another indication may be adduced by rendering apparent their 

 power of motion, as Dr. Bailey did : taking a portion of mud covered 

 with Closteria, and placing it in water exposed to light ; after a time, it 

 will be seen that if the Closteria are buried in the mud, they will work 

 their way to the surface, and cover it with ' a green stratum : this is 

 no doubt owing to the stimulus of the light exerted upon all matter, 

 although at first appearing very like a voluntary effort. Another is 

 afforded by their retiring beneath the surface when the pools dry up. 

 Mr. Ralfs states, that he has taken advantage of this circumstance to 

 obtain specimens less mingled with foreign matter than they would 

 otherwise have been. 



During the summer of 1854, the Rev. S. G. Osborne drew our 

 attention to the economy of an interesting specimen of this family, 

 the Closterium Lunula. After many careful investigations, we have 

 been enabled to satisfy ourselves that the membrane of the endochrome, 

 both on its inner and outer surface, is ciliated. 



In the Closterium Lunula, we have ascertained that the best view 

 of its circulation, and the cilia which give to it its impulse, are ob- 

 tained by the use of sunlight, transmitted through the combination of 

 coloured glass proposed by Mr. Rainey, and adapted to a l-4th achro- 

 matic condenser ; with which must be used a l-6th objective of Ross's. 



* The test for starch can be easily applied, and so remove any doubt that may 

 exist. It is only necessary to bear in mind that unless granular matter be seen in the 

 interior of the cell, starch cannot be present. A small quantity of diluted tincture of 

 iodine may be applied, removing the free iodine by the aid of heat, occasionally adding 

 a little water to facilitate its removal. This also will assist in the removal of the 

 brownish stain which at first obscures the characteristic purple tint; and then, by 

 applying the highest power of the microscope, the peculiar colour of the purple iodide 

 of starch can in general be easily perceived. 



