Natural Philosophy.— Optics. 389 
cubic inch of water did not contain less than 100 of these ani- 
mals. In the same view, and nearly at all times, the water was 
found filled with several different species, resembling in size 
some of the infusoria. Other animals of larger dimensions, 
and of many species, were equally constant, and, if less nume- 
rous, yet ten or twenty were always to be found within the 
space of a common tumbler glass. In all these cases the water 
was luminous. The light of the whole of these species disap- 
peared when they died, either from keeping the water too long, 
from warming it, or from the addition of spirits. Dr Mac- 
Oulloch has added upwards of 190 species to the list of lumi- 
nous marine animals. The most conspicuous among these are 
about twenty small species of Medusa, in addition to those al- 
ready known to be luminous. In the ancient genus Cancer, a 
considerable number of Squilloe were also found possessed of 
phosphorescence. In the genera Scolopendra and Nereis, five 
or six were luminous, which were all the species observed by 
Dr MacCulloch. The other known genera in which luminous 
species were observed, were Phalangium, Monoculus, Oniscus, 
lulus, Vorticella, Cercaria, Vibrio ; Volvox, to these Dr Mac- 
Culloch adds, among the fishes, a new species of Leptocephalus. 
The remaining luminous animals consisted of new genera, or 
at least of animals which could not be referred to any as yet to 
be found in authors. Dr MacCulloch seems to think, that the 
ling and other fish which inhabit the submarine valleys, at depths 
to which the light of day cannot penetrate, must perceive their 
food, and pursue their avocations, by the phosphorescence 
of their prey, or of the animals which abound in the sea, or by 
phosphorescence elicited from their own bodies. Dr MacCul- 
loch’s observations were generally made in harbours, but never 
at a distance exceeding eight or ten miles from land. See the 
Journal of Science , Literature , &c. vol. xi. p. 248. 
4. On the Phosphorescence of the Lampyris noctiluca and 
splendidula.—ln a curious paper on the Phosphorescence of the 
Lampyris noctiluca and splendidula , published in the Biblio - 
theque Universelle for May 1821, p. 52. M. Macaire has 
drawn the following conclusions from numerous observations 
1. A certain degree of heat is necessary to the voluntary phos- 
phorescence of these animals.— 2. Their phosphorescence is ex- 
