18 INTRODUCTION. 



continually in motion. Although two of these reasons apply 

 only to the genus Closterium, I freely admit that if the 

 Closteria can be proved animals, the question as to the other 

 genera will be decided. 



Few indeed hint at such a motive for adopting the opinion, 

 nevertheless I feel persuaded that the animal-like forms of 

 the Desmidieee have had a great, though not avowed, in- 

 fluence on the determination of this question. Did we trust 

 solely to the eye. we should conclude that objects so different 

 in form and variable in appearance, were far more like ani- 

 mals than vegetables. Their symmetrical division into two 

 segments ; the beautiful disciform, 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 characters seem in- 

 deed to pertain more to the lower animals than to vegetables. 

 We are thus induced, however unconsciously, to judge be- 

 fore examination, and we naturally search for arguments in 

 support of our preconceived opinion instead of those which 

 may elicit the truth. But experience has proved that form 

 alone is a most deceptive guide, the implicit dependence on 

 which has, in many similar instances, been the cause of 

 error ; and I believe that if a person unacquainted with what 

 has been written respecting the two groups should look at 

 the representations of the Desmidiese, and examine the grace- 

 ful and arborescent Zoophyte, having its branches to all 

 appearance loaded with fruit that is periodically produced, 

 matured, and shed, he would without hesitation place the 

 Desmidiese in the animal, and the Zoophyte in the vegetable 

 kingdom. Nor could we wonder at such a decision, since 

 in former times, even observers of high scientific attain- 

 ments, judging by external appearances, did in fact class 

 Zoophytes with the Algae. 



Again, Ellis, who first established the animal nature of 



