Jan. 6, 1881] 



NA TURE 



227 



obscures et les plus difficiles " (Comptcs rciidiis, t. vi. 

 1838, pp. 808-812). 



This, the first synthetic solution (of General Sabine's 

 address on presenting the Copley Medal) was published, 

 if we mistake not, in 1837. M. Bertrand, in his eloge of 

 Lamd (January 28, 1S78, Mcinoircs de I'Academie des 

 Sciences), says" M. Chasles obtenait, en la transportant 

 k la theorie si souvent iftudii^e de 1' attraction des 

 ellipsoides, des demonstrations et des re'sultats admirds 

 comme un modele d'dlegance et de gifneralitd" 



We have no space left, having perhaps already dwelt 

 too much in detail upon the complete works, to give an 

 account of the numerous papers we referred to above. 

 This is the less necessary as the results of many are 

 already incorporated in the larger works. We must how- 

 ever just mention the important mechanical principle 

 founded upon the proposition " quand deux polygenes 

 dgaux sont placds d'une maniere quelconque dans un plan, 

 il e.xiste toujours un point du plane qui est cgalement 

 distant de deux somnicts homologues quelconques des 

 deux polygenes, le point est semblablement place par 

 rapport aux deux polygenes.'' 



The applications of this, under Poncelet's form of 

 enunciation, are fully treated of by Richard in his " Note 

 sur un nouveau principe de cindmatique sur son emploi 

 et sur la Theoreme de M. Chasles" (Paris, 1856). 



In the closing lines of the Rapport M. Chasles indig- 

 nantly condemns the modern system which has for its 

 supreme and immediate object des applicaticDis pratiques ; 

 and which is " caracterisee suffisamment par I'idee fatale 

 de bifurcation." These remarks we pass over, but gladly 

 draw attention to a wish which he strongly expresses, viz. 

 that a defect should be remedied by the creation of two 

 chairs, one for " G^omc'trie infinitesimale et analytique," 

 and the other for "Analyse transcendante." If these 

 chairs do not now exist, it would be a fitting compliment 

 to his memory to establish one or both. One other wish 

 we have which we repeat, and that is, following the 

 fashion of the time, that a collected edition of his papers 

 be issued, for at present they are scattered over a very 

 wide area. 



In this notice we are indebted to the funeral speeches 

 pronoimced over M. Chasles's grave {Coiuptes rendus, xci. 

 No. XXV., December 20, 18S0) which, and M. Chasles's own 

 remarks, we have freely cited in their original language, 

 thereby securing conciseness of expression. 



We must however linger no longer by the grave, but 

 turn to the " living present," after repeating M. Dumas's 

 last words, " .Adieu, Chasles, adieu ! " R. Tucker 



PROF. HUXLEY ON EVOLUTION' 

 II. 

 T F all the Mammalia are the results of a process of 

 -'■ evolution analogous to that which has taken place in 

 the case of the Equidje, and if they exhibit different 

 degrees of that process, then a natural classification will 

 arrange them, in the first instance, according to the place 

 which they occupy in the scale of evolution of the mam- 

 malian type, or the particular rung of the " scala mam- 

 malium " on which they stand. The determination of 

 the position thus occupied by any group may, I think, be 

 effected by the deductive application of the laws of evolu- 

 tion. That is to say, those groups which approach the 

 non-mammalian Vtrtebrata most closely, present least 

 inequality of development, least suppression, and least 

 coalescence of the fundamental parts of the type, must 

 belong to earlier stages of evolution ; while those which 

 exhibit the contrary characters must appertain to later 

 stages. 



^ Ccntlnued frcm p. 204. By the courtesy of the Secretary of the Zoulo- 

 logical Society we are able to give the remainder of the paper "On the 

 Application of the Laws of Evolution to the Arrangement of the Vertebrata, 

 and more particularly of the Mammalia," by Prof. T. H. Huxley, F.R.S. 



Judged from this point of view, there can be no doubt 

 that the Monotremes embody that type of structure which 

 constitutes the earliest stage of mammalian organisa- 

 tion : — 



1. The mammary glands are devoid of teats ; and thus 

 the essential feature of the mammal could hardly be pre- 

 sented under a simpler form. 



2. There is a complete and deep cloaca, as in Verte- 

 brata lower in the scale. 



3. The openings of the ureters are hypocystic — that is 

 to say, they open, not into the bladder of these animals, 

 but behind it, into the dorsal wall of the gcnito-urinary 

 passage. As this answers to the neck of the allantois, the 

 ureters of the Monotremes retain their primitive embryonic 

 position. 



4. There is no vagina apart from the genito-urinary 

 passage, and the oviducts are not differentiated into 

 distinct uterine and Fallopian regions. 



5. The penis and the clitoris are attached to the ventral 

 wall of the cloaca. 



6. The epiphyses of the vertebrae are but slightly, or 

 not at all developed.' 



7. The malleus is relatively very large, and the "pro- 

 cessus gracilis," which is singularly long and strong, passes 

 between the tympanic and the periotic bones to the 

 pterygoid, with which it is firmly united. Thus the 

 palato-pterygoid apparatus is directly connected by a 

 " suspensorium " with the periotic, as in the Amphibia 

 and Sauropsida. As in these, the representative of the 

 incus is extremely small and that of the stapes columelli- 

 form. 



8. The coracoid is complete, distinct, and articulates 

 with the sternum. 



9. The hip-girdle is provided with large epipubes, and 

 the iliac axis is inclinecl at a large angle to the sacral axis. 



10. The corpus callosum is very small. 



11. There appears to be no allantoic placenta, though, 

 from the obvious remains of the ductus arteriosus and of 

 the hypogastric arteries, there can be little doubt that the 

 foetus has a large respiratory allantois. It is quite 

 possible that, with a large umbilical sac, there may be an 

 imperfect " umbilical " placentation. 



But, while the Ornitlwrliynclius and the Echidna are 

 thus the representatives of the lowest stage of the evolu- 

 tion of the Mammalia, I conceive.it to be equally unques- 

 tionable that, as Ilaeckel has already suggested, they are 

 greatly modified forms of that stage — Echidna, on the 

 whole, representing a greater, and Ornithorhynchus a less, 

 departure from the general type. The absence of true 

 teeth in both genera is an obvious sign of extreme modi- 

 fication. The long tongue, extraordinary external auditory 

 passages, and relatively large convoluted brain of Echidna, 

 and the cheek-pouches and horny mouth- plates of Orni- 

 thorhynchus, arc other indications of the same kind. 



Hence, the primary mammals which were less modified, 

 and the existence of which is necessarily postulated in the 

 conception of the evolution of the group, cannot, without 

 risk of confusion, be called Monotremata or Ornitho- 

 delphia, since in all probability they were as widely 

 different from Ornithorhynchus and Echidna as the 

 Insectivora are from the Edentata, or the Ungulata from 

 Rhytiiia. It will therefore be convenient to have a distinct 

 name — Prototheria — for the group which includes these, 

 at present, hypothetical embodiments of that lowest stage 

 of the mammalian type, of which the existing Monotremes 

 are the only known representatives. 



A similar reasoning applies to the Marsupialia. In their 

 essential and fundamental characters they occupy an 



' Dr Albrecht ("Die Epiphysen und die Amphiomphalie der Sjiugethier- 

 wirbel-kOrper : " Zoologis^tter Anzcigey, 1879. No. 18), while admitting that 

 Ec/tidna has no epiphyses, describes epiphyses of an incomplete character 

 between the posterior twelve caudal vertebra2 of Ornit/wrhynchus. _ So far 

 as I am aware, the memoir of which Dr. Albrecht has given a preliminary 

 notice, has not yet been published. I content myself therefore with remark- 

 ing that my own recent observations are in harmony with Dr. Albrecht's 

 statement. 



