116 FEE?HWATER ALOJ;. 



pleasing object, especially wlieu viewed by dark back -ground 

 illuraiuatiou. 



A further step towards more complex structure is traced in the 

 nearly allied Enteromorpha iittestinalis, which, in late summer, fonns pale 

 green tubular fronds, often a foot long, in similar habitats, and is found in 

 gi-eat abundance in warm pools in the " Black Countiy." Like 

 Tetmspora, it is a charming object, especially in a young state, and it 

 possesses further interest, as connecting the marine and freshwater 

 floras, being an inhabitant of salt marshes also, and leading up to several 

 species which are exclusively marine. 



To the same order as Protococcus belongs that most strange and 

 beautiful of all the lower vegetable organisms, Voh-ox globator, to which 

 the limits of this paper do not allow more than a passing reference. It 

 must suffice to remark that the analogy between Volvox and Protococms 

 will be more easily reahsed by conceiving a number of the gi'een cells of 

 the latter in their motile condition thickly and symmetrically embedded 

 in a larger glassy sphere, with the ciha ouly protruded. 



Volvox should be examined in cells shallow enough to prevent its 

 movement, and by transmitted light, in order to observe its structure ; 

 but its most lovely aspect is when it is viewed by powerful dark back- 

 ground illumination in a cell sufficiently deep to allow its exquisite pale 

 green crystal spheres, with their miniature Volvoces within, to maintain 

 their swift and graceful roUing motion across the field of the microscope 

 under low powex's, when it becomes an object of matchless beauty. 



It is not an abundant plant in this neighbourhood. The mthless and 

 wanton invasion of Sutton Park by a railway, and consequent filliug-up 

 of the well-known "Webb's Stews," have destroyed a constant habitat of 

 this as of several other choice plants, as well as the first known locahty 

 for the beautiful Kotifer Melicerta Tyro, discovered there last year by Dr. 

 Hudson. 



The distribution of Volvox seems to be capricious, for it often appears 

 in sufficient quantity to render the water pale green, then disappears as 

 suddenly, and perhaps only reappears months or years afterwards. 



There are, however, situations in which it appears every year, and 

 whore good specimens may bo obtained by straining a few pints of the water 

 through inusliu, and so, as it were, concentrating the spheres of Voh'ox, 

 which may then be washed off into a small bottle. If it is desired to 

 keep this plant in cultivation, all Entomostraca must be carefully removed 

 with the pipette, as they devour it greedily. 



For details of its structure and mode of rcj)roduction the student 

 should refer to the researches of Busk, Cohn, and WiUiamson, of which 

 a slight summary is given in the " Micrographic Dictionary." 



Before passing from the Unicellular Algro, wo must glance at one 

 other large order, which surpasses all others in variety and singularity of 

 form, in perfection of symmetry, and in brilliance of colom* — the 

 Dcsmidiacca;. 



