;o8 



NATURE 



[March 25, 1920 



either be continuous with that on the tarsus or 

 show stages in "breaks" at one or two of the 

 joints (Fig. 3). These and other facts of a hke 

 character go to prove that the degenerative- evolu- 

 tionary processes in the ostrich are all orfrto- 

 senetic in their nature, and that a retrogressive 

 change set up in any one direction is likely to be 

 continued until final elimination of the part in 

 question. The continuity is probably more apparent 



W\G. 3. — Series showing various stages in the loss of scales over the big toe. 



than real ; for if the somatic changes correspond 

 with alterations in the germ plasm, it must be in- 

 ferred that these are discrete in their origin, 

 and apparent continuity is conferred mainly by 

 intermixture and owing to the smallness of the 

 changes. The stages must, however, be succes- 

 sional and represent a definite tendency in the 

 germ plasm, in contrast to the haphazard nature 

 ■of the mutations usually studied — a tendency which 



is held to be wholly apart from any considerations 

 as to the welfare of the bird, as well as from 

 environmental influences. 



To the highly contentious question of the inherit- 

 ance of acquired characters, the ostrich would 

 appear to have a contribution to offer. Owing to 

 the loss of its second toe, the crouching bird, for 

 mechanical reasons, no longer makes use of the 

 symmetrical axial callosity at the ankle, but 

 develops an accessory one to the side. This is 

 formed anew with each generation, and must have 

 done so ever since the second toe disappeared, 

 though presumably this happened thousands and 

 thousands of generations ago. No hint of the 

 accessory callosity occurs on the newly hatched 

 chick ; it is not inherited, but has to be acquired 

 anew each time. On the other hand, the here- 

 ditary axial callosity, though unused for the same 

 period, shows no, signs of reduction; it has per- 

 sisted through the ages, though non-functional. 

 Further, the ostrich rests upon its sternal and 

 pubic projections, and a strong callosity is de- 

 veloped over each. These would unquestionably 

 form as a direct response of the skin to the pres- 

 sure and friction involved in crouching, but are 

 found to be hereditary, showing on the newly 

 hatched chick. Hence we are presented with an 

 hereditary structure which would also be formed 

 independently as a result of the ordinary activities 

 of the bird were it not already provided, strongly 

 compelling us to suspect that the presence of the 

 former is in some manner directly connected with 

 the latter ; in other words, that a character origin- 

 ally developed as a result of external stimuli has 

 in time become so impressed upon the organism 

 that it now makes its appearance apart from the 

 primary stimuli. 



The question of the origin of the three or four 

 species of ostrich also makes some appeal to the 

 evolutionist. No one intimately acquainted with 

 the northern and southern ostrich would dispute 

 their specific distinctness, but the East African and 

 Somali species appear to be founded on inter- 

 mediates of the two. Moreover, the northern 

 and southern birds freely interbreed, and their 

 offspring are fertile, some of the characters blend- 

 ing and others showing Mendelian segregation. 

 Unquestionably all the representatives of the 

 genus Struthio are a common stock, continental 

 in their distribution, in which mutations have 

 occurred in certain areas and not in others, but 

 not of such a nature as to prevent free inter- 

 breeding. 



The Conservation of Our Coal Supplies.^ 

 By Prof. J. W. Gregory, F.R.S. 



COAL is the main material foundation of British 

 industrial supremacy. The importance of 

 <;oal is given by Mr. Justice Sankey as his first 

 reason for its State ownership. The rapid British 

 industrial progress at the end of the eighteenth 



"^ Address to the Philosophical Society, Glasgow, on March lo. 



NO. 2630, VOL. 105] 



century was due to our abundant coal. Modern 

 coal mining began in Belgium earlier than in 

 Britain, but British mines soon had the greatest 

 output in the world. In 1800 they produced two- 

 thirds of the world's coal, in i860 the proportion 

 was 60 per cent., and in 1913 the United States, 



