406 MANIPULATION. 



Alga. — These are found abundantly both in salt and fresh 

 water; many of them form most interesting subjects for 

 microscopic examination, the marine species in particular, 

 being so often covered with Zoophytes of various kinds, the 

 ciliated arms and internal structure of whose polyps are 

 objects of such extreme interest. In a work like the present, 

 it would be impossible to point out aU the principal varieties 

 in either class; the author would, therefore, beg to refer 

 those who may be anxious to obtain correct information on 

 these subjects, to the excellent work of the Hon. W. H. 

 Harvey, termed Phycologia Britannica, or a History of British 

 Sea-weeds ; and to the British Fresh-water Algcs of Dr. A. JI. 

 HassaU. Amongst the algae, however, are now classed 

 an extensive family of microscopic plants, termed DesmidicEe, 

 for our knowledge of the British species of which we are 

 mainly indebted to the labours of Mr. Kalfs ; they have a 

 horny covering, and starch is a universal constituent of them. 

 Their principal genera are as follows : — 



Pentasterias, Closterium, Scenedesmus, 



XantBidium, Titmemorus, EoBinella, 



Euastrum, Micrasterias, Desmidium. 



Mosses. — The structure of mosses is one of extreme 

 interest ; the parts most frequently examined are the leaves 

 and the theca, or seed vessel, with its various appendages, 

 viz., teeth, calyptra, and operculum. Some specimens may 

 be mounted in Canada balsam after having been moistened 

 and then properly laid out between sheets of blotting paper, 

 to dry the thecse ; others, from which the operculum has been 

 removed, may be mounted on discs in the manner shown by 

 figs. 215-16-17, and one specimen in particular, named the 

 Funaria hygrometrica, when so mounted, will exhibit the move- 

 ment of the teeth, if the moist breath be allowed to come in 

 contact with them. The leaves of Sphagnum, or the bog-moss, 

 exhibit a cellulair structure, with a spiral fibre wound round the 

 interior of each ceU. The leaves of some species of Splachnum 

 and Hookeria are also remarkable for the elegance of their 

 appearance. The following genera will be found to include 

 the most interesting varieties : — • 



