162 FRESH-WATER ALG.E OF THE UNITED STATES. 



Plate CLV, figs. 1-8, normal forms capable of polymor- 

 phic contours at will ; figs. 9-15, cells contracting and com- 

 ing to rest, forming encysted sporular bodies; figs. 16-19, 

 encysted bodies in more advanced stages, dividing into 

 two and four parts ; figs. 20, encysted forms often in great 

 numbers; figs. 21, 22, sporaugial bodies ejecting microzoo- 

 gonidia. 



The encysted forms are often very abundant, forming a 

 thick scum, or floating crust. In this quiescent state the 

 cells have been mistaken for independent forms of algse. 

 Microcystis olivacea; M. Nottii; also Protococcus turgldus 

 and P. chalybius, of Kuetzing, are now regarded as repre- 

 senting variable phases of this resting condition of Euglena 

 viridis. 



The forms included in this genus have been most com- 

 monly classified with the Infusoria, but not without dissent. 

 Such authorities as C. A. Agardh, Kiitzing, also Perty, 

 Bergmann, Lenkhart and Carter, and more recently Cien- 

 kowski, Hansgirg and others, refer them to plants, the 

 Fresh- water Algae. Stein, the distinguished German au- 

 thority on Infusoria, recognizes organs he takes for mouth 

 and pharyngeal tract, which are essential to animal exist- 

 ence, but acknowledges that no solid food has been seen to 

 pass through these organs. Dr. Hansgirg thinks the organs 

 observed are not really mouth and throat, but serve a respi- 

 ratory office (respiration of water). They stand in connec- 

 tion with the contractile vacuoles and serve the function of 

 osmose and exosmose which in other algse, particularly some 

 of the OscUlariece are supposed to facilitate the power of 

 locomotion. 



Euglena have generally (not invariably) a red eye-spot 

 which has been taken to indicate animal life, but such is not 

 necessarily the case; the same red pigment spot is found 

 more or less frequent in most of the forms of Volvocacece. 



Am aware that Kent in his Manual of the Infusoria, tells 

 of some of the latest and perhaps most exhaustive exami- 

 nations made by himself, by keeping Euglena specimens for 

 a prolonged interval in water with finely pulverized car- 

 mine, and then discovered, by submitting them to a magnifi- 

 cation of 800 diameters, very small particles of carmine in 

 the body; but the question arises, could not these have 

 found entrance by absorption through the respiratory organs, 

 as suggested by Dr. Hansgirg? 



However this may be, they are so frequently observed 

 with recognized algse forms, we place them here until a more 

 unanimous opinion may be formed regarding them. 



