108 NATURAL HISTORY 



are shaken to the bottom of the water, they will rise 

 more rapidly, if the phial containing them be placed near 

 the light ; and also that no Entomoslracea^ , or larva, 

 especially those of the gnat, should be kept in the same 

 reservoir, as the latter will destroy them. 



The length of the specimens which I have examined 

 was about l-350th of an inch.: Ehrenberg gives l-280th 

 as their length. They are most numerous in spring and 

 summer. The magnifying power best adapted for view- 

 ing them, is from 300 to 500 times, in an achromatic; 

 with the latter powder, the long cilia of the mouth may be 

 distinctly recognized. 



184. Cercaria ruhrum. The red Cercaria. — The ani- 

 malcules of this species, which is new, I discovered in 

 September, along with the green Cercaria, from which 

 they do not differ except in colour, and in being rather 

 larger, with the cilia at the mouth more distinct ; 

 they change their form like the green ones, and often 

 assume a funnel shape, the base of the cone being hol- 

 low. The eye is very distinct, and of a light brown, the 

 body being of a rich garnet colour. They propagate by 

 a longitudinal division, for I have observed some of them 

 with the two heads distinctly separated. 



185. Cercaria spirogyra. {Euglena spirogyra, E.) 

 The spiral-dotled Cercaria. — This is also a new species, 

 of a green colour, wiih a circular body, but which it can 

 flatten at pleasure : two views of it, magnified, are shewn 



* See " Microscopic Cabinet," page 83. 



