44 INTRODUCTION. 



ounces of distilled water. Of other solutions, he says that they 

 " tend to destroy the colouring-matter of delicate objects, and 

 ultimately spoil them by rendering them opake*." 



To those who will read a book on this subject, it is quite 

 unnecessary to enter upon a formal vindication of the study 

 of the lower tribes of organized life. 1 shall content myself 

 with the observation that, whilst this study is not wanting in 

 those qualities which recommend the other branches of 

 Natural History as a means of intellectual improvement, it 

 has a peculiar claim on account of the light which it reflects 

 on the ultimate organization of living bodies in general. 

 Physiologists have of late pursued the investigation of the 

 structure and development of cells, both animal and vege- 

 table, with the greatest zeal ; and with good reason, since it 

 is obviously most desirable that we should thoroughly un- 

 derstand these elements of organization before we attempt to 

 explain its more complicated arrangements. For the attain- 

 ment of so important an object, the Desmidiese furnish the 

 most valuable assistance. If the view which I have taken 

 be correct, their frond, in most of the genera at least, con- 

 sists of a single cell, which, although it is certainly more 

 complex than cells in general, enables us to trace its own 

 history with ease and certainty, and reveals to us that of 

 forms still more simple. 



It may suffice thus briefly to show the utility of such in- 

 quiries ; but the improvements which the microscope has 

 received in modern times may well suggest a wider applica- 

 tion of the language in which the illustrious Ray vindicated 

 his favourite pursuits f. 



* Whilst my best thanks are due to Mr. Topping for this account of his mode 

 of preparing the cells, I must observe that the neat execution of them re- 

 quires more skill and leisure than most persons possess, and therefore presume 

 I shall render an acceptable service to my readers by mentioning that cells 

 of an)'^ shape or size that may be required, and also the thin glass necessary 

 for closing them, are supplied by Mr. Topping. In justice to Mr. T., whose 

 cells I have used extensively, I must bear testimony to their beauty and 

 utility. Misaddress is No. 1, York Place, Pentonville, London. 



-j- " Non deerit qui me vanse curiositatis arguat, qu6d res adeo viles et ab- 



