654 PROF. HUXLEY ON THE [DcC. 14, 



3. The openings of the ureters are entocystic ; that is to saj% the 

 ureters open into what is called the " hasc" of the bladder, in front 

 of the narrowed "neck" by which it passes into the tubular 

 "urethra." This means, I conceive, that, morphologically, the 

 bladder of the Marsupial represents the bladder of the Monotreme 

 + the anterior part of the genito-uriiiary passage— the so-called 

 " trigonum," if not more, of the bladder of the Marsupial, being the 

 homologue of that anterior segment of tlie genito-urinary passage of 

 the Monotreme. 



4. There is a distinct and long vagina, quite separated from the 

 cystic urethra, in the female ; and the oviducts are differentiated 

 into uterine and Fallopian portions, 



5. TJie penis is large, and the corpora cavernosa are connected by 

 fibrous tissue and muscles with the pelvis. The spongy body has a 

 large bifurcated bulb ; and Cowper's glands are verv largely de- 

 veloped. 



6. The vertebrae have distinct epiphyses. 



7. The malleus is small ; and its connexions are similar to those 

 which it possesses iu the higher mammals. The incus is relatively 

 larger, and the stapes more or less stirrup-sliaped. 



8. The coracoid is short, does not articulate with the sternum, and 

 becomes ankylosed with the scapula. 



9. The hip-girdle is provided with epipubes, usually of large size 

 and well ossified ; and the iliac axis is inclined nt a small angle to 

 the sacral axis. 



10. The corpus callosum is small. 



11. In the few forms of which the foetus is known there is no 

 allantoic placenta : while the umbilical sac is so large that the possi- 

 bility of the existence of a transitory umbilical placentation must 

 be taken into account. 



It will be observed that in the characters 1, 2, 3, 4, 5, 6, 7, 8, and 

 the latter part of the 9th, the Marsupials agree with the higher 

 mammals; while in the former part of the 9th, the 10th, and the 

 ,11th they present Prototherian characters. So far, therefore, they 

 constitute an intermediate type between that of the Prototheria and 

 that of the higher mammals, which may be termed that of the Me- 

 tatheria. And if there were any known animals which combined 

 these characters, with a complete double dentition, unmodified pen- 

 tadactyle manus and pes, and normal uterogestation, they would 

 furnish us with the exact transition between the Prototheria and the 

 higher mammals, which must have existed if the law of evolution is 

 trustworthy. 



No known Marsupial, however, possesses these additional cha- 

 racters. None has more than a single successional tooth on each 

 side of each jaw ; and, as Prof. Flower (to whom we owe the highly 

 important demonstration of this fact) has pointed out, the question 

 arises whether we have here a primary dentition with only one 

 secondary tooth, or a secondary dentition with only one tooth of 

 the primary set left. I have uo doubt that the answer given to 

 this question by Prof. Flower is correct, and that it is the milk- 



