20 GENEEAL HISTORY OF THE INFUSORIA. 



and to assimilate their organization -w^ith that he attributed to other Poly- 

 gastrica, represented the larger oil-vesicles and starch-grains to be either 

 stomach-sacs or ova, — at one time the one, at another the other, in a purely 

 arbitrary fashion. Some again of the more transparent or refracting vesicles 

 were, with no shadow of reason, called fecundating or spermatic glands. An 

 attempt to show the error of such an hypothesis of internal organization 

 would be futile and uncalled for at the present day. 



Habitats, Distribution, Appearance in Masses, and Vital Endoa\tvients 

 OF Desmidie^. Vegetable Nature and Affinities. Mode of Collection. — 

 The Desmidieae live in fresh water, in ditches and ponds, and rarely in 

 streams, except when these are very sluggish. They will often rapidly aj^pear 

 in a recent collection of water, and are not destroyed when the pool is dried 

 up, as their reappearance immediately after a shower proves ; nevertheless, 

 ponds which do not dry up dui^ing the summer, and pools in boggy ground, 

 are richer in these organisms, provided the water remains sweet. To quote 

 Mr. E-alfs's experience — " The Desmidieae prefer an open country. They 

 abound on moors and in exposed places, but are rarely found in shady woods 

 or in deep ditches. To search for them in turbid water is useless ; such 

 situations are the haunts of animals, not the habitats of the Desmidieae, and 

 the waters in which the latter are present are always clear to the very bottom." 

 They no doubt inhabit the fresh waters in all parts of the globe, for they 

 have been found wherever sought in each hemisphere. Still the several 

 genera and species are not universal, for, as in the case of higher plants, 

 some species are peculiar to one country, others to another ; and in the same 

 country the presence and prevalence of any one species wiU be determined 

 by the physical features of localities, by the nature of the soil, and the like. 

 The distribution, however, of the Desmidieae has not been inquired into so 

 fully as to justify any attempt to lay down special laws. 



Oftentimes in smaU collections of water, Desmidieae of the same or of 

 various species and genera multiply to such an extent as to colour the water, 

 and in the case of the filamentous species, to appear in filmy masses on the 

 surface or at the bottom of the pool ; still this enormous multiplication, and 

 the coloration of the water thej^ inhabit, are far less frequent in the case of 

 the family in question than with others — for instance, the Eugleneae, or even 

 the Diatomeae. 



Mrs. Thomas {op. cit. p. 36) has described the green masses formed by 

 Cosmarium, which duiing summer and autumn " would float to the surface, 

 rapidly disengaging oxygen as the sun shone on them, and sinking again to 

 the bottom with the coolness of the evening. Later in the year, masses would 

 adhere to the inner surface of the bottle in the form of a thin pellicle, or 

 collect in slimy masses, which appeared to dissolve with the warmth of the 

 coming spring. The green colour changed to that of a reddish yellow; and it 

 might have been thought that all was dead, did not the microscope show the 

 same beautiful green, both in young and fiill-groAvn plants, together with much 



bright red and brown, apparently the casings of the sporangia Large 



Cosmaria still in active motion (the remains of the mature growth of the pre- 

 ceding summer) lay imbedded in the mass, when a small portion was separated 

 for microscopic observation, as well as clusters of young ones (I. 13, 14). 

 When the bottle had remained more than a year untouched, except for change 

 of water, these masses increased in leathery hardness ; green life was not 

 extinct, but became feeble in colour, and too much changed to warrant further 

 observations, while a small portion placed in another bottle, and more freely 

 exposed to the light, multiplied with great rapidity." 

 • Many of the vital endowments of the Desmidieae have already been de- 



