some Marine Invertebrata. 187 



8. The light from the dead Noctilucae, or from fragments of 

 them, is identical with that from the vigorous living animal.—' 

 When the hght of the Nocttlucm, after frequent excitement^ be- 

 comes white, it is also more fixed, and finally covers the whole 

 body. From numerous experiments, M. de Quatrefages con- 

 cludes, that this kind of light is evidence of disease, or of a de- 

 cline of vigour, and when the light is universal, of death. Micro- 

 scopic examinations make it apparent that in these cases the 

 light is still made up of minute points, and it is evidently of the 

 same nature with the light given out in active life. 



9. Precautions necessary to succeed in the preceding observa- 

 tions.- — The animals should be examined without the use of a 

 compressor ; and care should be taken in employing high powers, 

 not to be deceived by the light proceeding from a point not quite 

 in the focus, whose rays produce a confused image, as if the light 

 were uniform instead of localized. This illusion is difficult to 

 avoid with fragments, as they are apt to be folded, so as to bring 

 more than one point of light in the focus at once. 



10. The phosphorescence is not the result of a kind of com- 

 bustion. — On taking a barometer tube nearly filled with mercury, 

 putting in some seawater containing Noctiluca (the water occu- 

 pied 6 centimetres of the tube, and the bed of Noctilucae was 

 3 centimetres thick), and then inverting it over mercury, a 

 phosphorescence was produced of the pale white light which indi- 

 cated approaching death, a consequence of the imperfect vacuum. 

 After one hour and eighteen minutes, the phosphorescence had 

 ceased, and could not be restored by shaking it. Oxygen gas 

 was introduced without efiect. It is probable that the phospho- 

 rescence, if due to combustion, would have been restored by the 

 oxygen, as happens with the Lampyri, according to Matteucci, 

 under similar circumstances. 



Four tubes were filled with water containing the Noctilucae. 

 Into one oxygen was poured, into the second hydrogen, the 

 third carbonic acid, the fourth chlorine. The first three gases 

 produced the same effect, and not more than atmospheric air 

 occasions through the agitation its passage causes. After haK 

 an hour these tubes were shaken with precisely the same result 

 in all. Chlorine acted like other irritating agents ; the light was 

 at first bright and continuous, but rapidly became extinguished. 

 Macaire and Matteucci have shown that the hght of the Lampyi-i 

 is immediately brightened in oxygen, and rapidly extinguished 

 by carbonic acid. The light therefore cannot be alike in origin 

 in the two cases, 



11. All physical agents that produce contractions cause phos- 

 phorescence, and in proportion to the intensity of the contractions. 

 — This conclusion was established by M. de Quatrefages by ex- 



13* 



