no 



the boundaries of species and of genera ? Do the isothermal lines 

 ever accurately bound the range of species, or are they altogether 

 independent of them ? What are the circumstances which render 

 certain rivers and certain mountain ranges the limits of numerous 

 species, while others are not ? None of these questions can be satis- 

 factorily answered till we have the range of numerous species accu- 

 rately determined. 



During my residence in the Amazon district I took every oppor- 

 tunity of determining the limits of species, and I soon found that 

 the Amazon, the Rio Negro and the Madeira formed the limits be- 

 yond which certain species never passed. The native hunters are 

 perfectly acquainted with this fact, and always cross over the river 

 when they want to procure particular animals, which are found even 

 on the river's bank on one side, but never by any chance on the 

 other. On approaching the sources of the rivers they cease to be a 

 boundary, and most of the species are found on both sides of them. 

 Thus several Guiana species come up to the Rio Negro and Amazon, 

 but do not pass them ; Brazilian species on the contrary reach but 

 do not pass the Amazon to the north. Several Ecuador species 

 from the east of the Andes reach down into the tongue of land be- 

 tween the Rio Negro and Upper Amazon, but pass neither of those 

 rivers, and others from Peru are bounded on the north by the Upper 

 Amazon, and on the east by the Madeira. Thus there are four 

 districts, the Guiana, the Ecuador, the Peru and the Brazil districts, 

 whose boundaries on one side are determined by the rivers I have 

 mentioned. 



In going up the Rio Negro the difference in the two sides of the 

 river is very remarkable. 



In the lower part of the river you will find on the north the Jac- 

 chus bicolor and the Brachyuriis Couxiu, and on the south the red- 

 whiskered Pithecia. Higher up you will find on the north the 

 Ateles paniscus, and on the south the new black Jacchus and the 

 Lagothrix Humboldtii. 



Spix, in his work on the monkeys of Brazil, frequently gives, 

 " banks of the river Amazon " as a locality, not being aware appa- 

 rently that the species found on one side very often do not occur on 

 the other, though the fact is generally known to the natives. In 

 these observations I have only referred to the monkeys, but the same 

 phsenomena occur both with birds and insects, as I have observed 

 in many instances. 



3. On the Anatomy and Development of Echinocqccus 



VETERINORUM. By ThOMAS HuXLEY, F.R.S. 



(Annulosa, PI. XXVIII. XXIX.) 



On the 25th of November, 1852, a fine female Zebra, whilst at play 

 within its paddock, accidentally broke its neck. The animal had 

 always appeared to be quite healthy, and it was in perfectly good 

 condition — but, upon examination, its liver was found to be one mass 



