Prof. Agassiz's Fish Nest

Cambridge, Mass., January 2. - Professor Benjamin Piercc, Superintendent ". the United Statea Coast Survey, has ju-.t. reoeived the following letter from Professor Agassiz, director of the Hassler expedition, detaüing the important disoorvery winch he has ímiJo while stcaming in the Guit' iStream : St. Thomas, December 15, 1871. My Dear Pitoi'KSSOR : For Bovera] days after we li.tt Boston I was greatly troubled by a sense of general Wttkneag, so much so that moro than once I thought I l : ! undertaken more than I had thu gtrength for. But as soon as we got into warmar hititudcs I feit botter and now I mu aotually improviug beyond niy condition at tlie start. As soon as vo reaehod thu Gulf Stream vo began to work. Indeed Ponrtales organizod a party to study the temperaturas as soon aa we ed (J:iy Head, and he will hinwelf n por( liis results to yon. which aro quito intereating My attuntion vas entiroly turncd to THE Gri.l'-WEED and its inbabitunts, of which we made extensivo colloctions. Our observations favor the view of those who boliuvo that the iloating woed is dcrived from planta torn from the roeks upon which sargassum naturally grows. I mado a vory siraple experiment which seems to me to seltlo the matter. Evory branch of the soaweed that is depri ved of its floats at onco sinks to tho bottom of the water, and these floats are not likely to bc the first parts developed lïoni the spores. Moreover, aftel' examining a very large quantity of the weed, I can say that I have notseen a branch however email which did not exhibit distinct marks of haviny been torn from a solid attachmont. DISpOVEEY OF A NEST OF Fisn. Yob may hardly feel an interest in my zoologioal observatious.but I am guro you will l)c pleased to learn that we had the best opportuuity of oarofully exaniining most of the animáis knowii to inhabit the Gulf-weed, and some which I did not know to occur nmong them. Ilowovcr, the most intcresting discovery of the voyage thus inv it the iinding of a nest built by fish, fioating on the broad ocean with its live En Lght. On the I3th of tho month Mr. Mansiiüld, ono of tho officers of the Haaaler, brought me a buil of Gulf-wccd whioh he liad just picked up, and whieh excitcd my curiosity to tbo utmost. It round massof sitrgassum, about the aize of twD lists, rolled up together. ïie wholo consisted to all appearanoe of nothing Init (iulf-wecd, tho bianchea and f wlüch were, however, ovidcntly knit tojrutlu.T and not only balled into a roundi sh nmss, for though somo of the ::i:d branches huug loose from the rest, it beoamo at once visible that the bulk of tbc ball was huid together by threads trending in nvory direotion among the sea-weeds, as if a co uplo ofhandfuls of branches of sargaa&um had been rollod up together with elastio threads trending in cvery direction. Put back into a lavge bowl of water, it beoamo apparent that thb masa of e :■..■ ida was a nest, the central pact of whioh was more closely bound up together in the form of a ball, with il loose brancheH extending in variojia direoüona, by whiali tho wholo was kept floating. TUF. NEST. . A tuore careful exninin: , soon revea] ; the fact that the elastio tbreads which held tha Gulf-weed togotht-r were beaded at intervals, sometiiuea two or Airee beada being closo togcther, or a bunoh oí' thcm haugiug from tbo same ■r of' threads, or they were more rarely soattered at :i greateraistanoe onofrom her. Xowhere was thciv rr.uch regularity observable in the distribution of ii" 1 ,:i'l-, eind thoy were t'ound scattered throughout the whole ball of soa-woeds px'otty uniformly. The beads themsolvea were about the Biza of an ordjnary pin's iiead. We had, no doubt, a nust before as of the most ourioiu kind, full of eggs, too, nuil t!ie eggs soattered throughout . maas of the nest and r.ct placed together in a oavity oí' the whole structure. WHAT WAS THE BUI] DES ': Wlint animal oould hare bv.ilt this singular nesi? was tho nest question. Itdid ü :i take ü'.ueh time to osoertain tho olasa of (lio anüual kingdom to whioh it "belongs. A coininon pocket lens at oneerevoaled two largo oyes up'ui tho sido of the head and a tail bent ovurthe back of the body, as the embryo nnitornily appeamin ordinary fishes shortly before tho period of' hatching. The many einpty ogg-cases observed iu tho nest gavo promise of an eai-ly opportunity of soeing somo embryos freeing fiemselvea from their envelops. Mean while a number of these cggs with the liva ombryos wsre cut out of the nest aad placed in separate glass j;irs to multiply the cb.an.ce8 of preserving them, while the nest as a wholo was seeured in aloohol ae a memorial of our unexpectoJ discovery. WII.VT THE EMBRYOS ARE. The nextday I fouud two embryos iu one of my glass jars. ïhey Ocoasionally ïuovcd in jerks and then remained for a long while luotionless apon the bottom of the jar. O.i the third dy 1 had over a dozen of tb e youug fishea in tay rack, tlie oldest of whieh begin to be more activo and proudse to afford further opportunities for study. I need not relal ■ in detail the evideace I soon obtaiaod that these cuiluyos were fishes. Sufiice it to say that the dorsal oord with its h oerc J built was readily visible, as wall aa '■ui na with its rays. in tho eyes the oolobomo had not yot been fully elosed, and blood curreirts vrero unmisi iküble apon the yolk bag. But what kind of fish w.is í bis ? About the timo of hatching the filis of this class of animáis differ too much from tllOSO of thfl a lult, and the general forin exliibits too few peculiariri':s, to afford auy olue to Üiis problem. I could only supposo that it would likely prove to bc one of the pelagic species ot the Atlantio, and of these the most oomniüi are exocetus, nauorataa, scopelus, ohironectes, gyngnethus, monacanthus, tetraodon, and diodon. Was there a way to eoine nearer to a correct solution o my doubts? THE TROBLEM SOLVIlll. As I had in formez years made a soniextrusive stndy of the pigment celjs of the skin in a variety of young fishes I niw resorted to this inethod to identify my embryos. Happily wo had on board several polagic tishoa alive, whioh could aíford mearía ot' comparison, but nnfortanately the steamer was shaking too much and rolling too heavily for microscopio d!. rrvaüim of even moderatoly high ers. Nothing, however, should bo loft untried, nul the vory first comparison I made seouved the desired result. The iigniL'iit cells of a young ohironoctes jnctus I idéntica] witli our littlo einbryos. !t ti.us stands as a well-aathenticated fact th;ii the comraon pulagio cliironootes of tho Atlantic (namod chironectcs piotue by Cuviev) builds a nest i'or its eggs in wliicli the progeny is WTapped up Wlth the materials of which tho nest itaelf ia oompo3od aa these m:iteriíil.s aro living Gul fweed, tho fish oradle, rooking upon the decp ocean, is oarricd along as an undying arbor, aiFording at tho saino timo protection and afterwards lood for its living freight.