1 66 NATURAL SCIENCE. Sept.. 



thinks that it is a clear case of the direct effect of the agency of 

 external circumstances to the exclusion of internal causes. It is, 

 however, obvious that even here internal causes are at work, although 

 the direct stimulus comes from without. M. de Kerherve himself 

 shows that, in the case of different species, the same external influences 

 operated differently : one of the factors is what may be called the 

 specific constitution. 



The Fossil Birds of La Plata. 



It may be remembered that in his account of the La Plata Museum, 

 in Natural Science at the beginning of last year, Mr. Lydekker 

 gave a brief description of the gigantic fossil birds of Patagonia, 

 which at that time were only imperfectly known through the writings 

 of Ameghino, Moreno, and Mercerat. Our knowledge of these 

 remarkable fossils has lately been greatly increased by a paper of 

 Ameghino's descriptive of a large series of bones, including all the 

 important parts of the skeleton (except the sternum) of several species 

 of the remarkable genus Phorovhacos. From this description it 

 appears that these birds, unlike the recent Ratitae, possessed heads 

 very large in proportion to the rest of the body. In the larger 

 species of Phorovhacos, P. longissimus, the skull is said to have been 

 upwards of two feet in length, and about ten inches high at the 

 hinder end of the beak. This latter was laterally compressed some- 

 thing like that of the Puffin, and was hooked at the tip. The 

 mandible, unlike that of nearly all recent birds, turned up at the 

 anterior end. It was originally stated that the jaws bore teeth, but 

 this is now found to be incorrect. 



The wing-bones were of the usual form, but proportionately very 

 small, so that it seems improbable that these birds were capable of 

 flight, though, no doubt, the wings were employed to aid in running 

 or, perhaps, in swimming. The ulna bears strongly marked impres- 

 sions of the insertions of the quills of the secondaries. 



The bones of the hind limb of one of the smaller species were 

 together about three feet in length ; the toes, of which there were 

 four, were armed with strong hooked claws. The posterior vertebras 

 of the tail did not unite to form a " pygostyle '' for the support of the 

 tail feathers as in the Carinatae, but remained separate from one 

 another, and are said to have been perforated by a notochordal canal. 



Besides Phorovhacos, several other genera are described, some 

 differing so widely that they will doubtless eventually be placed in 

 separate families. The name " Stereornithes " has been adopted for 

 these large birds from the Eocene (?) of South America, and it has 

 been suggested that Gastovnis and Dasovnis from the Lower Tertiary 

 deposits of England and France may be representatives of the same 

 group, which has been regarded as the ancestral stock of the living 

 Ratitae. It seems quite as likely that the Stereornithes are a group 

 of birds not necessarily closely related to one another, the members 



