75 



7. In the Sloths and Weasel.headed Annadillo the absence of the 

 os tincse, and the consequent formation of a single tube by the uterua 

 and vagina, approximate these organs veiy nearly to the oviduct of 

 thė Reptilia (see Owen, Zool. Proc. ii. 131, and on the Generation 

 of Marsupial Animals in Phil. Trans. 1834, p. 365). 



In the genera Bradypus, Dasypus, Manis and Myrmecophaga, 

 " the utero-sexual canal," to use the words of the last-quoted me- 

 moir, " is formed, as in the Tortoises, by a continuation of the urethra 

 or urinary bladder, into which the genital tube opens by a small 

 orifice." 



8. There is yet another highly important character, one indeed 

 whieh has probably a relation to the preceding, which displays the 

 intimate relationship of the Edentata and Reptiles, namely the ex- 

 treme simplicity of the brain. In the Armadillos, Manises and Ant- 

 eaters, the cerebral hemispheres are devoid of convolutions, whilst 

 in the Sloth they present a few anfractuosities (Owen, Phil. Trans. 

 1834, p. 361). 



9. Professor Owen gays, in bis elaborate memoir on the Mylodon 

 rohustus, that the presence of a persistent formative organ of the teeth 

 of the Megatheroids indicates a property in which they resembled the 

 Reptiles, viz. longevity (p. 166). And again, the intimate structure of 

 the soft dentine of the teeth of the Iguanodon resembles that of the 

 extinct Megatherium and of the recent Sloths (Owen's Odontography, 

 p. 251). Is it not an idea -vvhich forcibly impresses on us the unity 

 of the great plan of nature, that had a comparative anatomist existed 

 in the days of the Megatherium and Iguanodon, he might have dis- 

 covered from an examination of their teeth two comraon characters, 

 and might thence perhaps have inferred those very relations vi^hich 

 in the present paper I have been seeking to enforce vvith regard to 

 their congeners of another age — almost another world ? 



10. It is well knovirn that the blood-corpuscles of the Reptiles are 

 remarkably large ; the Sloths are the largest yet known amongst the 

 Mammalia, with the single exception of the Elephant. Perhaps 

 however this may be a character of little importance in elucidating 

 the natūrai affinities of groups, as we find the corpuscles of the Ar- 

 madillo rather smaller than Man's, and those of the Monotremata 

 of about the šame size as the human (GuUiver on Blood-corpuscles, 

 Zool. Soc, October 14, 1845). 



Sect. III. Ofthe Arguments adduced by Professor Oioen/or believing 

 the Edentata to be allied to Birds. 



I propose first to enumerate these arguments, and then to consider 

 them more particularly. They are to be found in Professor Ovven's 

 interesting papers on the anatomy of the Six-banded and Weasel- 

 headed Armadillos in the Proceedings of the Zoological Society of 

 London, so often referred to and ąuoted in this paper, and are as 

 follows : — 1, The presence of two caeca in the Dasypus 6-cinctus and 

 Myrmecophaga didactyla. 2, " The gizzard-like structure exhibited 

 in the tendinous external appearance and thickened muscular coat of 



