TRANSACTIONS OF SECTION D, 679 



An essential point, however, for us to consider is whether there are any 

 characters in animals or plants upon which the environment exercises no influence 

 at all or exercises such a slight influence that it may be safely neglected. 

 The method to adopt in order to settle this point would be to compare at a definite 

 period of their lives the statistics of variation in a family or population which 

 has been brought up under identical circumstances with a similar family or 

 population at the same period of life which has been brought up imder differing 

 circumstances. If this were done we could determine with considerable accuracy 

 the proportion of the variation of any character of the individuals that is due to 

 the environment and that which is natural and inherited. 



Unfortunately it is impossible to bring up a population under identical circum- 

 stances. If we take, for example, the individuals of a single hive of bees, which 

 have the same parents, pass through the early stages of their development in cells 

 which are almost identical in size and are regularly fed by the workers during 

 the whole of their larval life, there is still a considerable probability that the 

 individuals do not have a treatment which can, with any pretence to accuracy, be 

 called identical. The food that is collected by the worker-bees frequently comes 

 from varied sources or from flowers in diflerent stages of their growth, and it is 

 impossible to believe therefore that it has always identical nutritive properties ; 

 the larvie are not of the same age, and seasonal changes may affect the larvae 

 diflerently, some being checked in the early stages of their development more 

 than others. 



But even if we could, with justice, assume that the conditions of life for the 

 individual bees in a hive are identical from the time of hatching up to the time 

 when the adult characters are assumed, there still remain two sets of variable 

 conditions which must aftect the development independently of the influences 

 brought by the two parents in the germ-plasms. 



In the egg of the bee there is a considerable quantity of yolk, and this yolk is 

 the food material upon which the embryo is nourished throughout the earlier stages 

 of its development. There is no evidence that the yolk in the eggs of this or of 

 any other animal is constant cither in quality or quantity. On the other hand, 

 the extraordinary variations or abnormalities, as they are usually termed, which 

 the embryologist meets with in the segmentation of the egg suggest that there 

 are considerable differences in these respects between the eggs laid by a single 

 parent in a single act of oviposition. Moreover, the manner in which the young 

 eggs of the insects are nourished in the tubular oviduct before they are ready for 

 fertilisation gives very little support to the view that the amount of yolk deposited 

 in each egg is identical. 



The second consideration under this heading is possibly of even greater import- 

 ance. Vernon ^ has shown that the size and other characters of echinoderm larvse 

 vary very considerably according to the freshness or staleness of the conjugating 

 ova and spermatozoa. For example, he found that when the fresh spermatozoa 

 of Strongylocentrotus fertilised the eggs which had been kept eighteen hours of 

 the same animal, the larvte differed from the normal larvse, — 17'6 in body length and 

 — 15 per cent, in arm length, and when the fresh eggs are fertilised by spermatozoa 

 which had been kept eighteen hours the resulting larvae differed from the normal 

 by +11 per cent, in body length and by — 32'8 per cent, in arm length. 



This consideration is practically eliminated in the case of the worker-bees by 

 parthenogenesis, but it cannot be set aside in the case of the drones nor in the 

 cases of the broods of other animals which do not exhibit the phenomenon of 

 parthenogenesis. A comparison of the curve of variation of some character, common 

 to both, in drones and worker-bees from one hive would perhaps throw some light 

 on the general importance of this character. 



Before leaving this part of the subject, I must call attention to two results 

 bearing upon it, obtained by De Vrles in his botanical investigations, and related 

 by him in his very important work entitled ' Die Mutationstheorie.' This ob- 



' H. M. Vernon : ' The Eelations between the Hybrid 3-nd Parent- forms of Echinoid 

 I^arvffi. Phil. Trans. 1898, B. p. 465, 



