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Show 1892.] POSITION O F N O T O R Y C T E S T Y P H L O P S . 363 However, let us return to facts. Notoryctes occurs in the very middle of Australia, and every important part of its anatomy is known. Its teeth are not like those of any known Edentate, although they are aberrant enough in number and position even for Marsupials. It possesses a marsupium and an inverted inner angular process of the under-jaw-two characters which are together sufficient to prove that Notoryctes is a member of the Marsupialia or Metatheriain the sense hitherto defined and accepted. Mr. Douglas Ogilby1 has naturally and correctly placed Notoryctes as a separate family among the Polyprotodontia of the Marsupialia, but he hopes that " we have now obtained a definite link between the Proto- and Metatheria subclasses, a link which will perhaps eventually bridge over the gulf which at present separates the Monotremes from the Marsupials." A definite link would certainly, not perhaps eventually, bridge over that gulf, but unfortunately that much hoped-for link is still missing ; certainly it is not represented by Notoryctes. The Monotremes are characterized by the possession of:-(1) a typical cloaca; (2) a Saurian shoulder-girdle, i. e. an episternum or interclavicle, clavicles, complete coracoids, and considerable remnants of the ventral halves of precoracoids (epicoracoids of some authors). Additional characters are :-(1) absence of functional teeth in the adult; (2) a temporary marsupium without nipples. Notoryctes differs in every one of these four points from the Monotremes and agrees with the Marsupials. I. The cloacal arrangement appears at first sight strikingly like that of the Monotremes. The accompanying drawings (see p. 364) will explain the points better than a lengthy description. It must be borne in mind that there are Metatheria without a functional marsupium, while in the Prototheria this organ is functional; likewise there are monotrematous mammals besides the Prototheria. Marsupium and cloaca, taken alone, are therefore not sufficiently diagnostic for the separation of Proto- and Metatheria: they are differences of degree only, the intermediate links being furnished by the various Marsupialia themselves. I have shown elsewhere 2 that in the Marsupialia the urogenital and rectal openings are not completely divided off by a partition, there being still one common external opening which leads into a common, although mostly shallow chamber, viz. into the proctodseum or vestibulum cloacae. In both male and female Marsupials (figs. 4 and 6, p. 364) the urogenital sinus is still of considerable length, and is completely shut off from the rectum, while in the male Monotremes (fig. 1) the urine passes into a urodseum, or middle chamber of the cloaca above the penis. In Notoryctes and in all other Marsupials, this separate exit of the urine and of the genital products is made impossible by the completion of the fold F. Urine and sperm pass through the penis in the male, and in the female the ovarial products (eggs or foetus) have the same channel as the urine. This channel is the same in 1 Advance copy of portion of ' Handlist of Australian Mammals,' issued July 31st, 1891 : Sydney. 2 " Remarks on the Cloaca and on the Copulatory Organs of the Amniota," Phil. Trans. 1887, pp. 6-37, pis. 2-5. |
