OCR Text |
Show 104 ON CLASSIFICATION. Tl1 e 0't1 Le~• rop tera , InsedivoJ'a ' and Rodentia agree with Man . · . I)lacenta which is not only a 1nuch " discoidal," 1n possessing a ~ ~ f h · a 11 owance b e1· no0· made for the short r . urv. o t. o utenno wall.s , as hI.s , b n t also entirely res robl.e s dh 1 'd In be1ng dev loped m con J·U De tw' n with ~a d cidua. . Th1s ec~ u.a a1 w ays correspon. ds to at least the decidua serot21~a of Man~ fr quo~tly thero Is a well-developed decidua rejlexa. * II ow far a demdua vera can be said to be developed i doubtful. 1 am well aware that th se stat m nts ar in direct opposition to some that have been v ry confidently pnt forward. Thus, Professor Owen, in argujng a:)·ain t the views ont.ertained by Milne-Edwards and Gervm , mak s the followmg assertions :- "The degree of re m blance in outward form Letween tho placenta of the Rat or Har ., n the n haul, and th JJfycetes and Macacus on the other, m... t m to be more than counterbalanced by tho di~ renee f ·tructur . The ped~mc'ulate an:d cotyloid placenta of the Bat consists of frEtal pctrts exclu- Fig. 42. - ··-"-. .. / . ' ,, f f a Fig. 42.-!lfagnified Yi w of a section of the placenta and utcrns of a pregnn.nt HaL s~.v ely; the maternal at·eola'r port~·o n tt·s as d 2·s t~ ·n c t f r.0 1n it as it is in the cotyledon of the Rurninant, and is a persistent st1·ucture of * ce upon this subject the r c ntly-puhh. h d va1 u ab l e sa y of. Reichfie rt : 3 "BeitriiO"e zur Entwi.C kelung ·-gescln. chte <1 s lVI ersc 1l W m· e 11 n:;. " R. cJChe.r t nos 1 0 a complete, or almost compl te, detJidtut reflexa m· R a t ·, Ml'C • Gumoa-p1gs-,t ' almly Ba.ts; while in Rabbits, Hares, and amivorct, tllc decidua rejle.w only pm H:t ::;mTounds the ovum. THE PLA.CEN'J.1A. OF THE RAT. 105 the uterus. The discoid placenta of the monkey in lud a J ~ proportion of maternal cellular struc~ure, whi h ?~ · way w:th the footal portion. The difference 1n the orga~1 1nt rbl nd1ng of the circulatory organs of mother and offspnng, b. tw en th Rodentia and Quadr·umana, is of much more real 1mp rtanco than the degree of superficial similarity."-L. c., p. IG, n te. Led by the extraordinary contradictions of m of th best-known facts of embryology* contained in the pa sage * Eschricbt d escribcd the placenta of the Rat with great precision, ns the follow· in()" extract will show, six-and-twenty years ago. Is it possible that a hasty p rusal ot a passage which I have put into italics below ~hould have mi lc~l any of bis successors into supposing that Rodents have persistent cotyledons hk those of Ruminants?-" Placenta fere circularis erat; diametrus longior ex lineas cum dimidia explebat, brevior sex lineas. Superficies ovo obvcr a nonnihil con ava emt, cxterna autem sat convexa, ita uta margine ad centrum scnsim in tumulum surgeret et crassitudinem placentre ad duas lineas aug ret. In super:ficic ju concava, ovo obversa, tres distingui potuerunt regiones; cii·cum c utrum, a v, is umbilicalibus perforatum, laminulfl. illa pertenui obtecta rat, quam va a urnbilicalia hie circumdure jam observatum est. Circa peripberiam scabro a app, ruit, quasi fila seu vasa abrupta fuissent, in media regiono autem inter pcriph ricam ct ccutralem levis erat tunica sat distincta vestita. Superficies placcntre externa convexa duas regioncs obtulit. Peripherire propior inroqualis ad axern longitudinal m ovi latior crat, unam et quartam linero partem cxplens; ad latera angustior quartam modo linere partcm explens. Sic media et lrovis bujus superfici 'i r gio ovoidea quidem erat ut tota placenta, sed cum axe majorc transverse ei in iden . In cumulo hujus superficiei permagnum vas ab utero centrum placentro perforavit. Haud procul a centro quinque vasa minora intervallis sat requalibus utcrum cum placenta jungebant. Superficiei uterinro proxima placentro pars in lamella facile <lividcbatur, profundior autem pars eundem ilium laminarum innum rabilium contextum exbibuit quem in placenta felina fusius supra dcscripsi. Laminula a centro ad peripheriam sat regulariter ordinatas esse observare mihi vi u urn. Inter laminulas illas eandem esse alternationem laminularum footalium et utcrinarum vix dubitaro potui, prrosertim quum non modo vasa umbilicalia cd ab alt ra parte sex vasa majora ab utero placentam ingredi vidi em. At uterum examinan nova orta est dubitatio. Uteri cornua antequam ova excisa fuissent, moniliformin. apparuerunt, et inter singula ova fortiter constricta. Ita non modo numerus ed otiam forma. ovorum extus apparuit quid quod etiam placentro facillimo ob rvari videbantur. Intumescentiro, ova includentes, ipsro quidem oviformes crant, sed ad marginem superiorem ad insertionem ligamentorum latorum ct ante eadem singulre tumuli speciem prrobebant, placentam ap rte indicanti . Itaque placcntro in utero mm·is ratti non modo quoad footum, sed etiam quoad ut rum certum occupat locum, et embryoncs omnes in una serie in oppo itis ut ri cornibus symmetrice collocati sunt, utrum autem capitibns prroviis abdominibusque abdomen matl"is respicieutibus, an .clunibus prreviis dorsisquc nbdomini ~1atris obvcrsis inquirere neglexi. Ve1·um tumuli placentas indicantes non ip m iuerunt placentre. Ovis excisis iidem tumuli in utero rcmancbant ut tub r ula fusca tres lineas crassa, cliametrurn quinque linearum cxhibentia. Quo<l quum |