EwARi' — Variation : Gei'minal and Environmental. 355 



individual may not be settled, but undoubtedly more occurs than the laying of 

 the foundations. Subsequent to conjugation there is considerable scope for 

 variation in the size, colour, vigour, &c., of the new individual, as there are 

 possibilities of various changes of the germ-cells prior to conjugation. All 

 the variations in the germ-cells up to the moment of conjugation, together 

 with the variations during development and growth, I shall refer to as 

 Environmental Variations. 



ENVIRONMENTAL VARIATION. 

 I. — During Development. 



It will be convenient first to consider environmental variations beginning with 

 those that occur during development. By variation I understand difference in 

 structure, habits, &c., between the offspring and their parents. These differences 

 may be innate, i.e. have their roots iu the changes in the germ-cells prior to 

 conjugation, or they may be acquired after conjugation owing to every individual 

 being plastic enough to respond, up to a certain point, to external stimuli. 

 Further, these differences, whether germinal or environmental, may be established 

 at birth, or they may appear at any period of the life-history, and some of the 

 new departures may be handed on to the offspring of a subsequent if not the 

 succeeding generation. 



Hitherto it has been usually assumed that all congenital characters are trans- 

 mitted to the offspring. But, if by congenital is meant characters pertaining or 

 belonging to the individual at birth, this assumption is unwarranted: for, in 

 addition to hereditary characters pertaining to the germ-plasm, i.e. inherited 

 through the male and female germ-cells, and new characters created during 

 conjugation, there are various characters acquired during development of a purely 

 environmental and not necessarily transmissible nature. 



In certain families a dwarf appears at irregular intervals. We rightly, I 

 think, account for the occasional appearance of a dwarf by the principle of 

 heredity — it is a case of recurring germinal variation. But all dwarfing is 

 not due to hereditary influences ; it is sometimes, though congenital, purely 

 environmental. It may, e.g. be entirely due to an insufficient supply of 

 nourishment. 



Some time ago I found in a wild rabbit twelve young, eight in one uterus, 

 four in the other. All the eight in the one uterus were of uniform size and quite 

 as advanced in their development as the four (also uniform in size) in the other 

 uterus, but they were only half the size. When the eight were placed in one 



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