376 



Prof. St. G. Mivart. On the 



[Feb. 16, 



duction of the mouth of the cloaca of the female ef fc, Euproctus, into 

 an intromittent organ is also startling, and even amongst mammals, 

 the female of the spotted hyaena with its enormous clitoris, perforated 

 by the urethra, is wonderfully different from that of the striped hyaena, 

 otherwise so nearly resembling it in structure. The disconnexion 

 of the ureters with the bladder is a very important difference, 

 certainly, but even in placental mammals those ducts shift their 

 position greatly, as may be seen if we compare Sorex with 

 Hyrax. 



Moreover, it must be admitted that if the Monotremes had remote 

 Sauropsidan ancestors (as can hardly, I think, now be questioned) 

 then more or less of epicoracoids, interclavicles, &c, must have been 

 " in their blood," so that reversion is conceivable. Nevertheless, 

 I am far from believing that such a reversion has actually taken 

 place. Granted that degradation frequently occurs, yet it would 

 hardly, I think, get so completely on the old lines again. There 

 is, however, I venture to believe, another less improbable hypo- 

 thesis which I will now venture to suggest. It is the hypothesis 

 that the Monotremes come from a radically distinct stock from that 

 whence all other mammals proceeded ; that the Monotremes are 

 an example of hypothetical higher mammals in the making, the 

 future evolution of which may probably be hindered by man's 

 presence, but which, did they appear, would produce mammalian 

 forms more or less parallel to but, of course, radically distinct 

 from, the placental and marsupial series of mammals. The latter 

 series of mammals — the superior mammals — may still be supposed to 

 have arisen from Amphibia-like root forms, according to the position 

 defended by Professor Huxley, for which I think there is a great 

 deal to be said. The Monotremes, or inferior mammals, on the other 

 hand, must, I think, be supposed to be derived from Sauropsidan 

 ancestors, and according to this view the resemblances which exist 

 between these higher and lower kinds of mammals, including tooth 

 structure, will be induced resemblances — the two groups having 

 grown alike through the independent origin of similar structures. 



What evidence is there that the Amphioxus is a degraded animal ? 

 What principle of evolution need hinder us from regarding it as a 

 possible parent of another line of Vertebrates profoundly different 

 from the Vertebrates which have come into being ? Each of these 

 suppositions is alike hypothetical, and a number of similar dilemmas 

 may be suggested in cases more or less parallel. 



With regard to the Monotremes, however, we have a very solid 

 reason for regarding them as mammals which have arisen from another 

 root from the higher (placental and marsupial) Mammalia, namely, 

 the fundamental difference which, according to Professor Gegenbaur, 

 exists between their mammary glands and the mammary glands of 



