HABITS AND LATIN NAMES OF BRITISH PLANTS. 
421 
cavities, which is only an accidental occurrence. The origin of the cavities, as 
well as their sudden and traceless disappearance in the saline matter, in the 
interior of the cavity of the animalcule, can be as easily perceived as the forma¬ 
tion of one of those globules; and indeed sometimes the formation of such a 
cavity may be observed around the ingested globule, which again after some 
time disappears. The microscope shews that the cavities possess no special 
membranous walls, but consist of mere excavations of the saline substance ; they 
also remain for the most part near the inner surface of the membrane which 
forms the skin of the animal, and sometimes increase so much in size, that the 
cavity of one of the vesicles will occupy from one-third to one-half of the cavity 
of the entire animal. That these cavities contain a thin and watery fluid, and 
are not at any time filled with air, is evident from the strikingly small refraction 
of the rays of light on their edges; and in the larger Infusoria it is very plainly 
seen that they have no external opening. Similar cavities are formed in the 
mucus of the cells of plants, and are especially frequent in the immersed 
Confervoe. 
My botanical labours prevent my attending fully to these objects, but the, 
preceding remarks may be sufficient to lead naturalists to the further investigation 
of a subject demanding great perseverance, for the leading facts are not to be 
seen immediately in every Infusoria ; and these animals are sufficiently im¬ 
portant, for already have the Polygastrica been received into all our new 
zoological works. 
ON THE HABITS AND PECULIARITIES OF BRITISH PLANTS, 
AND ON THE DERIVATIONS OF THEIR LATIN NAMES. 
By T. B. Hall. 
(Continued from p. 349.) 
Cakile. —According to Hooker, an old Arabic word applied probably to this 
or some allied genus. 
Calamagrostis. — KxXx^xypusis, from K xXx^os, a Reed, and A ypusts, a genus of 
Grasses. 
Cakile maritima , Sea Rocket.—It is a common annual on Sandy sea-shores, 
flowering from J une to September, and making a very ornamental appearance. 
It abounds with alkaline Salt, and has the pungent mustard-like flavour of its 
class. 
