14 DEVELOPMENT. 



as life departs. The same phenomenon is exhibited by the hydroid, helianthoid, and asteroid 

 polypes. If a bunch of one of the bushy corallines, such as Sertularia ahietina, be plunged 

 when alive and active into fresh water or spirits, a gorgeous display of living stars is instan- 

 taneously produced. So also with Pennatula phospJiorea* 



The Ught of the Medusae, as Spallanzani observed, is not given out by all parts of the 

 body indifferently, but only by certain structures. Spallanzani states that when he cut off 

 the margins of the Pelagia phosphorea to a depth of from 5 to 6'", the border continues to 

 shine, which is not the case with the disk, and he attributes the phenomenon to the produc- 

 tion of a phosphorizing mucus by the light-producing parts. Ehrenberg regards the hght as 

 an act of organic life. He observes that "the active organic phosphorescence appears 

 frequently periodically, produced either spontaneously, or by excitement, frequently as 

 rapidly produced sparks, resembling small electric discharges. This repeated sparkling 

 converts a mucous, gelatinous fluid, which is discharged more abundantly during the operation, 

 into a secondary state of phosphorescence, which continues for a time, even after the death of 

 the organism, or after the severing of its parts." He considers the mucus enveloping the 

 ovaries as particularly susceptible, when in a fresh state, to this imparted phosphorescence. 

 In Oceania pileata he observed the light emanate from the locality of the ovaries, which, 

 being pendant in the centre of the sub-umbrella, illuminated the animal as an argand lamp 

 illuminates its glass shade. In Thaimantias hemispharica he observed the light to be given 

 out by the bulbous bases of the tentacula, which formed a garland of sparks of fire around 

 the circumference of the umbrella. Macartney had previously noticed, as we have seen, that 

 in this naked-eyed species, the light was given out from the same spots, and, he adds, from 

 the centre also. I have observed that in Thaumantias lucida the light was invariably given 

 out by the bulbs of the tentacles, and so also in other species of the same genus. In the 

 Bianea appendiculata, which is a beautifully luminous species, the phosphorescence is of a 

 greenish hue, and appears to radiate from the reproductive glands. In the Mediterranean I 

 have seen a large Mesonema give out rich flashes of flame from the bases of its numerous 

 marginal tentacles. Both Spallanzani and Tilesius have noticed that the Hght in the higher 

 Medusce shone most vividly during the contractions of the umbrella. 



Taking one fact with another, it would seem that the phosphorescence in the naked-eyed 

 Medusae is developed by the reproductive and motor systems : how, we cannot say. 

 Ehrenberg has concluded that the production of the light is " a periodical vital act dependent 

 on the nervous system, and similar to the development of electricity." But this can only be 

 regarded as an hypothesis. We have no clear evidence yet of the presence of a nervous 

 system in these animals. 



Development. — When treating of the reproductive organs of these animals, I discussed 

 the ovarian and spermatic glands ; but the naked-eyed Medusae do not reproduce their 

 species only in the normal fashion, i. e. by fecundated eggs ; several of them are now known 

 to multiply their kind by gemmation, little ones springing out almost ready made from the 

 substance of their parents, as Minerva budded on the creative brain of Jupiter. This mode 



* See a notice of the phenomena exhibited by this zoophyte when phosphorescing, in the second 

 edition of Dr. Johnston's British Zoophytes. 



