ACALEPHiE.-THE MEDUSAD.E. 



XXVll 



niiiigiiial lilanieiits, eight lulie-coverud eyes, four 

 ovaries, four chambers, four fringed arms, widi a 

 ceiUra! and four lateral openings. 



As a type of this group may be iustanced tlie Aure- 

 lia aurita (Lamarck, the Cyanea atirita of Cuvier), or 

 Aiiriculated Aurelius, which abounds in the waters of 

 tlie Baltic, and has been made the subject of special 

 study by the Swedish naturalists. 



In the same group we find the Pelagia cyanella, 

 with its globose body, and eiglit marginal tentacles ; 

 the Pehirjia noctiluca, a transparent, glass-like disc of 

 a reddish brown colour, very plentiful in tlie Mediter- 

 ranean ; and the Pelayia panopyra, an inhabitant of 

 the tropical seas. 



Many species of the Medusadce are phospliorescent, 

 and the luminous appearance presented by the ocean, 

 frLMjuently compared to a sheet of many-coloured 

 fl.inie, is due to the peculiar light-eujitting faculty of 

 these remarkable creatures. 



The class of Discopliorae may be divided into four 

 orders or families : — 



The Ilydraida; — having single, naked, gelatinous, 

 sub-cylindrical, but very contractile stems, mutable in 

 foim; the mouth fringed all around with a single series 

 of granulous filiform tentacula. 



The Sertulariidie — plant-like, horny polypiers, 

 rooted and variously branched, filled with a semifluid 

 organic substance, and the polypes contained within 

 sessile cells which are disposed along tlje sides of the 

 njain stem or branchlets, but are never terminal. Indi- 

 vidually they have no digestive cavity; one stomach is 

 common to the numerous group I 



The Modusadse — already described as possessing 

 an umbrella-shaped disc, provided with maiginal 

 tentacles, and eight lobe -covered eyes, four ovaries, 

 Cflls, and fringed arms, one central and four lateral 

 openings. 



The SiphonophorEe — wherein the animals are two- 

 fold and bell-shaped, fitting into one another. 



Of the Hydraid* and the Sertulariidie we speak 

 elsewhere ; our remarks in the present section will 

 still be confined to the Medusadce. Their aspect, as 

 seen by the poetical observer, is elegantly described 

 by Michelet, in his delightful volume of facts, fancies, 

 thought, and emotion, "La Mer:"^ 



" Among the rugged rocks, the laguues or pools left 

 by tlie receding tide were filled with little animals, 

 wliicli had been too slow to overtake the retiring 

 waters. Some shells were there, folded up in them- 

 selves, and suflering from exposure to the dry air. In 

 the midst of them, shell-less and without an asylum, 

 and fully e.xpanded, lay the living umbrella, which 

 naturalists have so inappropriately named lifediisa. 

 But why was so terrible a name bestowed on this 

 attractive being? I had frequently had my attention 

 arrested by these castaways, which one sees so often 

 on the sea-borders. This one was not larger than my 

 liand, but singularly pretty, with soft light shades and 

 of an opaline while, which melted, like a cloud, into 

 a tender lilac-coloured crown. The wind had over- 

 turned it. Its chaplet of lilac tresses floated above, 

 and the delicate umbel (that is, its proper body), find- 

 ing itself beneath, clung to the rock. Shuddering 



throughout its delicate substance, it was sorely 

 wounded and torn in those delicate hairs which are 

 its organs of respiration, absorption, and even of love. 

 All its substance, thus reversed in position, received 

 the direct rays of the Provencal sun, so keen and 

 severe at its first rising, and rendered keener by tlje 

 breath of the mistral which blew at intervals. This 

 double shaft transfi.xed the lucent creature. Living 

 in the bosom of the sea, whose touch is ever caressing, 

 it needs no armour of resistant epidermis, like the 

 terrestial animals; it receives everything to the quick. 



" AVas it dead or dj'ing? I could not make up my 

 mind that it was dead ; I maintained that it lived. At 

 all hazards, it would cost but little trouble to remove it 

 from the rock and deposit it in the adjacent pool. To 

 tell the truth, I felt some repugnance at touching it. 

 The delicious creature, with its transparent innocence 

 and its rainbow of soft colours, was like a trembling 

 jelly — glided, and escaped from my fingers. How- 

 ever, I slipped my band underneath if, carefully lifted 

 U]) the motionless body, whence all tlie filaments fell 

 back info their natural position wdien the animal is 

 swimming. In this manner I transferred it to the 

 neighbouring water. It sank, without giving any sign 

 of life. 



"I walked about the shore, but in ten minutes 

 returned to my Medusa. It was undulating under the 

 wind. It positively moved itself, and rose to the sur- 

 face. With singular grace its tresses floated under it, 

 and softly moved it from the rock. It did not go very 

 i|uickly, but still it went, and soon I saw it a long 

 way off." 



The Medusse are found in every sea, floating with 

 unconcern on the surf\\ce of the swelling waves. 

 Their locomotion is singularly slow, and indicates a 

 very feeble muscular energy ; nevertbelcss, what is 

 wanting in quickness is compensated by its contiimily. 

 Since their specific gravity considerably exceeds that 

 of the element in which they are imnierged, and since 

 their softness of substance precludes their reposing 

 on solid ground, it is necessary they sliould agitate 

 constantly in order to keep themselves afloat. AVh. n 

 they rest they sink. They are also compelled, by 

 the nature of their organization, to maintain a con- 

 tinual state of contraction and expansion, of systole 

 and diastole. 



We are told by Spallanzani, who examined their 

 movements with careful accuracy, that those of trans- 

 lation are accomplished by the edges of the disc 

 approximating to such an extent that the diameter is 

 very perceptibly diminished. . This etl'ort forces out a 

 certain quantity of the water absorbed in the body with 

 more or less violence, and consequently projects the 

 body in the inverse direction. Ueiuvigorated by the 

 cessation of force in its first state of development, 

 it again contracts itself, and makes another step in 

 advance. 



When the body is perpendicular to the lioiizon, 

 these successive movements of contraction and expan- 

 sion cause it to rise upwards ; when it is more or less 

 oblique, they elTect its advance more or less liorizon- 

 tally. If the animal would descend, it has only to 

 cease its etforls, and its descent results from its specific 



