The Zoologist — September, 1873, 8699 



deduction, even if it were correct in the fact, which I maintain it is not, that 

 the marsupial and placental trpes have had to struggle under similar circum- 

 stances. Mr. Darwin lays it down that the controlling forces which direct 

 the path of variation in a species are the other species with which it has to 

 struggle ; and if these forces were sufficiently definite and restricted in their 

 action to produce two such similar dental types as those of the thylacine and 

 dog, independently of each other, it strikes me that classification of mammals 

 would no longer be possible ; should we not have dogs, cats, rodents and 

 ruminants arising from independent sources all over the world ? Darwin 

 himself says (' Origin of Species,' chap. xiii. p. 413), "I believe that some- 

 thing more is included ; and that propinquity of descent — the only known 

 cause of the similarity of organic beings — is the bond, hidden as it is by 

 various degrees of modification, which is partially revealed to us by our 

 classifications." The writer sums up by saying that "it is just as probable, 

 external circumstances being similar, that the isolated marsupial ancestor 

 should give rise to carnivorous, rodent and herbivorous forms, as that they 

 should have developed from a placental type." Does he mean that because 

 one thing is as probable as another, that in any way explains why both 

 things should have taken place '? When the first discoverers of Pitcaim's 

 Island were accosted by one of the natives asking them iu broken English to 

 throw him a rope, would he think it a good explanation of this fact to have it 

 suggested to him that it was just as probable, external circumstances being 

 similar, that such a simple form of speech should have been developed from 

 the needs of isolated human nature on Pitcaim's Island as in England? 

 I think his mind would hardly be satisfied by such an explanation. — F. H. 

 Balkwill. 



lakes Albert and Tanganyika. — Sir Henry Piawlinson has received and 

 published in the ' Times ' a letter from Sir Samuel Baker, dated Khartoom, 

 July 2, entirely confirming, as far as Sir Samuel's opinion may be trusted, 

 the statement copied from the ' Telegraph ' into the August ' Zoologist ' 

 (S. S. 3639). Sir Samuel expresses a hope that he will be in England in 

 September. In reference to the oneness of Lakes Tanganyika and Albert 

 Nyanza, he says : — " The envoys sent by M'tese all assured me that the 

 Tanganyika is the M'wootau N'zize (Albert Nyanza) and that Ujiji is on 

 the eastern border ; that you can travel by boat from Ujiji to the north end 

 of the Albert Lake ; but you must have a guide, as some portions are very 

 narrow and intricate. From my experience of the high water-grass, 

 I should expect islands and floating vegetation in the narrow passes 

 described. I am by no means fond of geographical theories, but the 

 natives' descriptions were so clear that I accepted as a fact that the Tan- 

 ganyika and Albert Lakes are one sheet of water, with marshy narrow 

 straits overgrown with water-grass, through which you require a guide." 

 Sir Samuel's letter is of great length, and contains many details of his wars 



