Sep., 1890. 
WEISMANN S THEORY OF GERM-PLASM. 
205 
ON WEISMANN’S THEORY OF THE CONTINUITY 
OF THE GERM-PLASM. 
( Concluded from page 178.) 
The theory certainly gains support from observed cases, 
for amongst animals that propagate themselves by partheno¬ 
genesis or other asexual means do not vary, for instance those 
Saprophytes that have been so ably investigated by Dr. 
Dallinger. It occurred to me that his experiments would 
throw much light on the question, and I fortunately had the 
opportunity of asking him how these monads multiplied, and 
under what circumstances the variations, which he so success¬ 
fully obtained, took place. He kindly informed me that they 
usually multiplied by fission with occasional sexual genera¬ 
tions ; but that no variations or deformities occurred, except 
at the sexual generations. This would seem to prove that 
the former proposition, that unicellular organisms may be 
altered by the environment, is incorrect. If no change 
occurred during multiplication by fission, the environment 
apparently had no share in the wonderful changes necessary 
to accustom a species to a temperature ninety-seven degrees 
above the normal, except to select suitable variations as they 
arose at the sexual generations. 
One great objection to the theory is the difficulty of imagin¬ 
ing how all the variations, necessary among highly developed 
forms for a single step forward, can arise simultaneously. 
Take for example the oft-quoted instance of the giraffe. Let 
us suppose that an increase in the length of the neck has 
been brought about by some fortuitous variation, whereby 
the creature is enabled to reach higher zones of the foliage of 
trees than its contemporaries, and by so doing to triumph 
over them in the struggle for existence. This lengthening of 
the neck, though the most striking of the changes that must 
take place, is only one amongst a multitude that are necessary 
to make it beneficial. In the first place, additional bulk 
means additional weight, thus throwing strains upon parts 
that have not previously experienced them, upon the shoulders, 
upon the vertebrae of the neck and back, the fore-legs, etc., 
etc., which must be proportionately strengthened, and their 
attendant muscles with them. Before this can be done, the 
circulation must be augmented to supply the bones and 
muscles with blood in larger quantities to keep pace with the 
increased expenditure. Further, greater calls will be made 
upon the nerves that stimulate the blood supply, and they 
will have to be modified in harmony with the new require¬ 
ments. If now we have the modification of the neck alone, 
