548 



NA TURE 



\Oci. 25, 1877 



gentlemen cannot be charged with committing themselves to an 

 hypothesis '■Uhe most distant from the phenomena it attempts to 

 explain. " 



Now if it can be shown that the germs of disease are subject 

 to the same laws as other living things and exliibit similar 

 phenomena, and further, that without the inference tliat tliey are 

 endowed with vital properties, it is impossible to unravel the 

 most striking character which they present to us for consideration, 

 viz., the fact that they reproduce their kind, then I think there 

 is more reason for following up, in all its intricacies, the germ 

 theory, than to start with an assumed catalysis, molecular motion, 

 and a glandular matrix, as suggested by Dr. Richardson. 



Starting, then, from the indisputable fact that the materias 

 morbi of every communicable disease reproduces its kind, I have 

 considered this a primary law, and have tabulated other laws 

 which are associated with living beings by which it will, I think, 

 be found that there is a parallelism of a kind to attract and rivet 

 attention, especially, too, when many otherwise inexplicable 

 circumstances bend to this hypothesis. 



Primary Law of Reproduction, by which all living things 



reprodiiee their hind. 



Secondary Laws. 



Objective Laws. 



1. The diffusion or dispersion 



of germs. 



2. Their static existence. 



3. Limited duration of active 



existence. 



4. Period of development, 



maturity, and decay. 



5. Intermittent reproduction. 



Subjective Laws. 



1. Seasonsof activity. 



2. Climatic influence. 



3. Relation to latitude. 



4. Subjection! 



forces. 



5. Influence of locality. 



physical 



Without amplifymg this subject, which would carry me far 

 beyond the limits of an ordinary communication, I will only add 

 that though the above tabulation is very imperfect, there is quite 

 sufficient for any one who will follow out the ideas conveyed by 

 it to trace the intimate relation that exists between living beings 

 and the germs of disease. I would refer finally to the fact that 

 many diseases in men and animals have yielded 'up living germs 

 as their cause, chiefly, I may add, skin diseases it is true ; but 

 aphtha,^ closely associated with diphtheria, is, I think, acknow- 

 ledged by all unprejudiced persons to have. its origin m an 

 unmistakable and demonstrable germ. John Grove 



The Zoological Relations of Madagascar and Africa 

 Without entering into the details of this very difficult ques- 

 tion I wish to be allowed to state some of the general reasons 

 which have led me to a different conclusion from Dr. Ilartlaub,' 

 and also to point out where he has not quoted my opinions with 

 perfect accuracy. Instead of saying that " the fauna of Mada- 

 gascar is manifestly of African origin," my actual statement is as 

 follows ; — "We have the extraordinary fauna of Madagascar to 

 account for, with its evident main derivation from Africa, yet 

 wanting all the larger and higher African forms ; its resemblances 

 to iNIalaya and to South America ; and its wonderful assemblage 

 of altogether peculiar types " ("Geog. Dist. of Animals," vok i. 

 p. 2S6). My reasons for believing in the " main derivation" of 

 the fauna from Africa can only be understood by considering the 

 theory, now generally admitted, of the origin of the fauna of 

 Africa itself. All the higher mammalia are believed to have 

 entered it from the northern continent during the middle or latter 

 part of the tertiary period, and the occurrence of Psittacus and of 

 forms supposed to be allied to plantain-eaters and to Liptosjmiis 

 in the miocene of France, render it probable that many of the 

 peculiar groups of African birds had their origin in the old 

 PalKarctic region. Now Madagascar presents many cases of 

 special aflSnity with .South Africa, especially in insects, land- 

 shells, and plants ; and if we suppose it to have formed part of a 

 .South African land before the irruption of tlie higher mammals 

 and birds from the north, we shall I think account for many of 

 its peculiarities. Such facts as its possessing Potamochixrus and 

 the recently extinct Hippopotamus, while it has thirteen or fourteen 

 peculiarly African genera of birds against four or five that are 

 peculiarly Oriental ; of its having many African genera of lizards 

 and tortoises ; of its butterflies being decidedly African ; of its 

 numerous African genera of Carabidce, Lucanidje, and Lamiidte ; 

 while the specially Oriental affinities of its mammals, reptiles, 

 » See Medical Times, 1851, vol. u. p. 95. 

 ' Nature, vol. xvi. p. 498, and the Ibis for July, 1847, p. 334. 



and insects are hardly if at all more pronounced than the South 

 American affmities of the same groups, — all seem to me to warrant 

 the general conclusion that the " main derivation" of the Mada- 

 gascar fauna is from Africa. 



Dr. Ilartlaub speaks of my " attempted parallel between 

 Madagascar and Africa, and the Antilles and South America " 

 in such a way that his readers must think I had dwelt upon this 

 parallel in some detail as being special and peculiar. The fact 

 is, however, that I have always referred to it in a very general 

 way. At p. 75 vol. i. I say : " The peculiarities it (the JIalagasy 

 sub-region) exhibits, beings of exactly the same kind as tho.se 

 presented by the Antilles, by New Zealand, and even by Celebes 

 and Ceylon, but in a much greater degree." And again, at 

 p. 272, vol. i., I speak of it as "bearing a similar relation to 

 Africa as the Antilles to Tropical America, or New Zealand to 

 Australia, but possessing a much richer fauna than either of 

 these, and in some respects a more remarkable one even than 

 New Zealand." This mineral comparison with the two other 

 great insular sub-regions is, I think, justifiable, notwithstanding 

 great differences of detail. There is in all a rich and highly 

 peculiar fauna, a great poverty of mammalia, and a total absence 

 of many large families of birds characterising the adjacent 

 continent, together with special points of resemblance to distant 

 continents or to remote geological periods. 



It seems to me that such a problem as this cannot well be 

 solved by means of a group which, like birds, do not require^ an 

 actual land-connection in order to reach a given country ; and, if 

 all land animals are taken into account, tlie evidence does not 

 appear to warrant the supposition of a recent land-connection 

 of Madagascar with India or Malaya. At a very remote epoch 

 such a connection may have taken place, but if we are to give 

 any weight to the general facts of distribution as opposed to 

 those presented by birds only, the union of Madagascar with 

 South Africa is more recent and has had more influence on the 

 character of the Malagasy fauna. The numerous and very 

 remarkable points of affinity between Madagascar and South 

 America in almost every group except birds, are not alluded to 

 by Dr. Hartlaub, yet they would equally well support the notion 

 of a former u-nion of those two countries independently of Africa. 

 It seems, however, more consonant with our general knowledge 

 of distribution to consider these as cases of survival of ancient 

 and once wide-spread types in suitable areas ; and this is a 

 principle that must never be lost sight of in attempting to solve 

 the problems presented by such anomalous countries as Mada- 

 gascar. Alfred R. Wallace 



Selective Discrimination in Insects 



Your correspondent S.B., in hisletter in Nature of yester- 

 day's date, must be referring to some short abstract only of my 

 lecture on flowers and insects. I quite agree with him that 

 odour is very important in attracting insects, and dwelt upon it 

 in my lecture, as well as in my little book on " Flowers and 

 Insects." A striking illustration is afforded by night flowers, 

 which often become peculiarly odoriferous towards evening, as 

 has been already pointed out by various observers. 



S.B. attributes, I think, too little importance to the colouring 

 of flowers, but his letter shows him to be a careful observer, and 

 I hope he will continue to devote his attention to the subject. 



He would find H. MuUer's "Blumen und Insekten" a mine 

 of most interesting and accurate observation. 



London, October 19 John Lubbock 



Protective Colouring in Birds 

 With reference to the statement in my " Naturalist in 

 Nicaragua," p. 196, that the macaw "fears no foe," &c., the 

 well-known geologist, Prof. Gabb, sends me the following infor- 

 mation : — "I willingly comply with your request to repeat the 

 statement about the A'ukong pum; or macaw hawk of Costa Rica. 

 Not having your book by me now I cannot refer to page nor 

 quote your statement exactly. But as I recall it, you speak of 

 the great red and blue macaw as being so well defended as to 

 need no protective colouring, and that no hawk dares attack it. 

 In this you are mistaken. Not only have I seen on several 

 occasions heaps of the unmistakable feath-ers of the bird in the 

 woods, left in the manner that all woodsmen recognise as hawk's 

 work, but I have the statements of various Indians, not in collu- 

 sion, confirming each other, and finally I have had the bird 

 pointed out to me (I am not sure but that it|may occur in the col- 

 lection I sent to the Smithsonian). It is afaur-sized hawk of dark 



