TRANSACTIONS OF SECTION D. 1045 
has been unable to obtain satisfactory spectroscopic results, apparently from its 
feebleness. 
Besides Noctiluca, which was chiefly met with in inshore water, Mr. Murray, of 
the ‘ Challenger, describes various species of Pyrocystis,! a closely allied form, and 
indeed some of which have been thought to be identical with the former. They 
abound in the open sea, and are the chief causes of its phosphorescence in the 
tropical and subtropical oceans. The light is stated to proceed from the nucleus, 
and in this respect it diverges from that observed by De Quatrefages in Noctdluca, 
When shaken in a glass, they give out, Sir Wyville Thomson observes,’ the 
uniform soft light of an illuminated ground-glass globe. 
Dr. Giglioli, during the voyage of the Italian frigate ‘Magenta,’ mentions * 
that another division of the Protozoa, viz., the Radiolaria, show phosphorescent pro- 
perties. In the Pacific the genera Thalassicolla, Collozoum, and Spherozoum, 
shone with an intermittent greenish light. It is possible that Dr. Baird,* in his 
earlier paper, refers to the same group when describing an unknown phosphores- 
cent pelagic organism. 
No group of marine animals is more prominent in regard to phosphorescence 
than the Czlenterates. The Hydroida are familiar examples,’ and, as Mr. Hincks 
observes, none excels the common Obelia geniculata, which forms pigmy forests 
on the broad blades of Laminariz all round our shores. In the fresh specimen a 
touch during summer causes a large number of luminous points to appear on the 
zoophytes, the stems most irritated emitting beautiful flashes, which glitter like 
faintly-dotted lines of fire, the points not being harshly separated, but blending 
into each other, while the shock imparted by the instrument detaches the minute 
medusoids, which scintillate upward from the parent stem to the summit of the 
water. Mere blowing on the surface in July, where Laminariz abound, suffices to 
produce the-emission of light from the pelagic buds. Moreover, these minute 
bodies, along with the various species of Ceratiwm and minute larval forms of 
diverse kinds, are sometimes swept by the gales landward, and cause phosphores- 
cence where least expected. In the same manner Vaughan Thompson ° found 
luminous patches on the masts and windward yard-arms on board ship, and they 
gradually mounted upward as the gale increased. Many of the free gonosomes of 
the Hydroids are as luminous as the polypites, and indeed have been described by 
some of the older naturalists as one of the main causes of the luminosity of the 
ocean. The light in these (e.g., Thawmantias) gleams round the margin and along 
the four radii. 
The Ascraspedote Meduse have also been signalised as factors in producing the 
eerie of the sea, such forms as Pelagia noctiluca and Pelagia cyanella 
eing especially prominent. Spallanzani, indeed, made an elaborate series of 
experiments on the luminosity of the Meduse in his voyage to the Two Sicilies. 
Some of these, as Dactylometra (Pelagia) quinquecirra, Agassiz, are nocturnal in their 
habits. They are only occasionally found floating at the surface during the day, 
while at night, in the same localities, the bottom swarms with these large masses 
of dull phosphorescence, moving about with the greatest rapidity.” Species of 
Rhizostoma were likewise observed by Giglioli to have a pale bluish luminosity. 
The two most abundant Meduse of our eastern shores, viz., Aurelia aurita and 
Cyanea capillata (both in its young purple and adult brown condition), so far as I 
can make out, exhibit no luminosity. This agrees with the views expressed long 
ago by Ehrenberg. 
The oceanic “Hydrozoa (Siphonophora) are likewise characterised by their 
1 Proc. Roy. Soc. vol. xxiv. p. 553, pl. xxi; and Narrative, Zool., vols. i., and ii. 
p. 935-38. 
2 Atlantic, vol. ii. p. 87. 
* Atti della R. Accad. delle Sc. di Torino, vol. v. 1869-70, p. 492. 
4 Loudon’s Mag. Nat. Hist. vol. iii. p. 312, fig. 81, ¢, d. 
5 Even after many days and in impure water some of these retain this property, a 
shock to the stem sending off a crowd of luminous points from the tropbosome. 
® Zoological Researches, vol. i. part i. mem. iii. p. 48. 1829. 
7 Agassiz, North American Acalephe, p. 49. Cambridge, 1865. 
