In such a country we have a number of vegetable-feeding Ungulates, all of which present minute variations as to the length of the neck.

If, as Mr.Darwin contends, the natural selection of these favourable variations has alone lengthened the neck of the giraffe by preserving it during droughts; similar variations, in similarly-feeding forms, at the same times, ought similarly to have been preserved and so lengthened the neck of some other Ungulates by similarly preserving them during the same droughts.
(2.) It may be also objected, that the power of reaching upwards, acquired by the lengthening of the neck and legs, must have necessitated a considerable increase in the entire size and mass of the body (larger bones requiring stronger and more voluminous muscles and tendons, and these again necessitating larger nerves, more capacious blood-vessels, &c.), and it is very problematical whether the disadvantages thence arising would not, in times of scarcity, more than counterbalance the advantages.
For a considerable increase in the supply of food would be requisite on account of this increase in size and mass, while at the same time there would be a certain decrease in strength; for, as Mr.Herbert Spencer {28} says,[23] "It is demonstrable that the excess of absorbed over expended nutriment must, other things equal, become less as the size of an animal becomes greater.

In similarly-shaped bodies, the masses vary as the cubes of the dimensions; whereas the strengths vary as the squares of the dimensions."....

"Supposing a creature which a year ago was one foot high, has now become two feet high, while it is unchanged in proportions and structure--what are the necessary concomitant changes that have taken place in it?
It is eight times as heavy; that is to say, it has to resist eight times the strain which gravitation puts on its structure; and in producing, as well as in arresting, every one of its movements, it has to overcome eight times the inertia.

Meanwhile, the muscles and bones have severally increased their contractile and resisting powers, in proportion to the areas of their transverse sections; and hence are severally but four times as strong as they were.