ACALEPH7E. 



45 



gastric cavities in medusa aurita as subser- 

 vient to the same function. These sacs com- 

 municate directly with the gastric cavities by 

 means of openings in the membranous par- 

 titions which separate them. The partitions 

 bear on their inferior surfaces, plaited mem- 

 branes, which, under the microscope, present 

 the appearance of being studded with vesicles 

 containing a little watery fluid. A row of 

 filamentary organs is also attached to these 

 membranes, which move like external cilia, 

 even for some time after they have been re- 

 moved from the body of the animal. 



VI. Secretion. The existence of this func- 

 tion in the acalephae is made known to us by 

 the emission from their bodies, under certain 

 circumstances, of a glairy mucus ; by the 

 stinging effect which some unknown product 

 of their organization has upon our skin ; and 

 by the remarkable phenomenon of luminousness, 

 which a large number of them present. The 

 organs by which the mucus is secreted have 

 not been satisfactorily observed. Dr. Milne 

 Edwards saw reason to conclude with regard 

 to the rhizostoma, that a large quantity of this 

 fluid is secreted by a glandular structure 

 situated along the margins of the arms. The 

 stinging property possessed by several animals 

 of this class has been the subject of inquiry 

 since the time of Aristotle, but to this day 

 we remain in doubt with regard to the nature 

 and mode of production of the agent which 

 causes this effect. Some men seem to be in- 

 sensible to the irritation generally produced by 

 the contact of living acalephae. But, for the 

 most part, a slight touch of any part of their 

 surface, and chiefly of the pendent tentacula, 

 is followed within a few minutes, at most, by 

 a burning pain, redness, swelling, and some- 

 times even a vesication, of all that portion of 

 the skin which touched the animal. Sloane 

 said of the physalus, (" what the seamen call 

 caravels, or Portuguese men-of-war,") " They 

 burn violently they do suck themselves so 

 close to the skin that they raise blisters, and 

 cause sometimes St. Antony's fire."* Even on 

 our own coasts, severe cases of inflammation 

 of the skin are occasionally seen, which have 

 been produced by the irritation received during 

 bathing from some of the larger pulmograda. 

 In physalus, the stinging property seems to 

 reside chiefly in the fluid with which the ten- 

 tacula are filled. It continues to act power- 

 fully even after the organs containing it have 

 been detached from the body. And not only 

 so, but it is said by some observers that its 

 peculiar properties are so permanent, that 

 vessels in which the animals have been placed 

 must be washed several times in water, and 

 carefully scoured before they can be used 

 without inconvenience. On one occasion it 

 was found that linen, which had been merely 

 rinsed in soap and water, had this quality of 



' Nat. Hist, of Jamaica, ii. p. 273. Sloane re- 

 commends acajou oil as " the remedy for the sting- 

 ing of this nettle." Mr. Bennett has lately found 

 (Load. Med. Gaz. xiv. 908.) that the application 

 of vinegar to the irritated surface in some degree 

 alleviates the pain. 



irritation fifteen days after it had been used in 

 making observations on the physalus.* None 

 of the cirrigrada hitherto examined possess 

 the stinging property. 



The organs by which the luminous matter is 

 elaborated are unknown. In some species, it 

 is evidently mixed with the mucous fluid, 

 which is so abundantly poured out from the 

 margins of the arms and the disc. It has been 

 frequently observed that the ciliograda are 

 luminous chiefly along their rows of cilia, and 

 that these continue to emit light for some time 

 after their removal from the body. Perhaps 

 the greater number of the acalephae are lumi- 

 nous. According to Dr. M'Culloch, all 

 inhabiting the British seas are so ; and 

 indeed it is chiefly to the emission of light 

 by animals of this class that the beautiful 

 phenomenon of the luminousness of the sea 

 is owing in all situations. Spallanzani, 

 however, whose observations and experiments 

 on this subject were as extensive as they were 

 careful and ingenious, came to the conclusion 

 that " the medusae which are possessed of lumi- 

 nous properties are extremely few compared 

 with those which are destitute of it." The 

 same philosopher remarked, with regard to 

 some of the pulmograda, that they emit light 

 more strongly during the contractions of their 

 disc than at other times ; that the intensity of 

 their light increases when they are pressed in 

 any way ; that the luminousness resides chiefly 

 in a peculiar fluid secreted by glands situated 

 around the margins of the disc, along the edges 

 of the tentacula, and in the fringed partitions of 

 the gastric cavities ; that this fluid being mixed 

 with other fluids, as with fresh and salt water, 

 and especially cow's milk, imparts its lumi- 

 nousness to them ; that when spread over solid 

 bodies it continues to shine for several minutes; 

 and that in it there generally exists that irri- 

 tating substance which produces the stinging 

 effect. Spallanzani applied some of this fluid 

 on two occasions to the tip of his tongue. It 

 excited a burning sensation, which lasted more 

 than a day. A similar feeling, but much more 

 painful, followed the accidental application of a 

 singledrop of the same fluid to the conjunctiva.f 

 In most of the acalephae, the external cover- 

 ing is very fine, smooth, and delicate; but 

 sometimes it is granular, or even warty. It 

 does not appear that these differences in its 

 structure have been observed by any naturalist 

 to be connected with corresponding differences 

 in the power of emitting light. (See LUMI- 

 NOUSNESS, ANIMAL.) 



VII. Generation. The organs of this func- 

 tion cannot always be satisfactorily ascertained. 

 This may, in a great measure, be owing to their 

 minuteness and transparency when not in 

 action. Ovaria and oviducts, however, are dis- 

 tinctly seen in several species; but no other 

 organs connected with the generative function 

 have hitherto been discovered. According to 

 Eschscholtz, the ovaria in the physograda con- 

 sist of several groups of vesicles and filaments, 



* Journ. Roy. Inst. 1831, p. 205. 

 t Travels in the two Sicilies, iv. 250. 





