110 Prof. Owen on the Echidna Hystrix. [Mar. 2, 



A bifid obtuse rudiment of penis or clitoris projects from the fore part 

 of the single urogenital or cloacal aperture, and in advance of the base of 

 the tail-stump. 



The brain, of which the largest part was the mesencephalon, chiefly 

 consisting of a vesicular condition of the optic lobes, had collapsed at this 

 part, leaving a well-defined elliptical fossa of the integument, indicative of 

 the widely open fontanelle at the upper part of the cranium *. 



The skin of the shrunk body showed folds, indicative of the originally 

 plump, well-filled abdomen. 



The fore limbs, in their shortness and breadth, foreshowed the charac- 

 teristics of those of the parent, which may be said, indeed, to retain in this 

 respect the embryonic character, with superinduced breadth and strength. 

 The digits have already something of the adult proportions, the first or 

 innermost of the five being the shortest ; the others of nearly equal length, 

 but graduating shorter from the third to the fifth. The characteristic dis- 

 position of the digits was better marked in the hind limb, the second 

 already being the strongest and longest, the rest more rapidly shortening 

 to the fifth than in the fore leg. The innermost, agreeably with the law 

 of closer retention of type in the embryo, though the shortest of the five, 

 was less disproportionately so than in the adult. 



After entering into other particulars, and quoting from correspondence 

 on this subject of animal physiology, the author summarizes the chief 

 points in the generative economy of the Monotremes, which still remain to 

 be determined by actual observation as being 



1 . The manner of copulation. 



2. The season of copulation. 



3. The period of gestation. 



4. The nature and succession of the temporary structures for the 

 nourishment and respiration of the foetus prior to birth or exclusion. 



5. The size, condition, and powers of the young at the time of birth or 

 exclusion. 



6. The period during which the young requires the lacteal nourishment. 



7. The age at which the animal attains its full size. 



In respect to the second point : as the female Echidna with the young, 

 described in the present paper, was captured on the 1 2th of August, she 

 might be impregnated at the latter end of June or in July. Females 

 therefore, killed in the last week of July and the first week in August, in 

 the province of Victoria, would be most likely to afford the capital facts 

 noted under the "fourth" head, viz. the impregnated ovum in utero, 



* In observations and illustrations of the development of the brain in Marsupialia 

 (Phil. Trans. 1834), it is shown that, in the Kangaroo, some time after birth the chief 

 and largest part of the brain is the luesencephaton, that the cerebellum is not more ad- 

 vanced than it is in Batrachian Reptiles, and that the cerebral hemispheres are even less 

 developed : amongst the figures illustrative of this stage of formation of the marsupial 

 brain is one of a dissection of the rudimental hemisphere, showing the large and simple 

 ventricular cavity then occupying it. 



