On Growth and Form by D'arcy Thompson is a somewhat tricky case. (The last word of the title is "Form" not "Forms" by the way.) The first edition was published in 1917, and is therefore out of copyright in the US. The expanded edition ws published in 1942, and will be in copyright IN THE US until 2037, unless the copyright holder failed to renew the copyright in 1970 (after the initial 28 year term). Actually the renewal could have been anywhere in the period 1969-71, as a 1 year margin plus or minus was allowed. Assuming that the renewal was done properly, any images included in the first edition are free for anyone to use. Any added in the 1942 edition are not.
If Wikipedia lists the image you want as public domain, check the detailed reason that they give. For the image of figs 517 & 518 from the 1942 ed The original publication date is listed as 1917, which implies that the image was in the first edition.
Wikipedia is pretty good at copyright, but has been known to get things wrong. In fact I have been involved in correcting a few errors of this sort. In this case verification is not excessively hard.
I would suggest that you find a copy of the first edition, and check if the image you wan to use is included there. If it is, you should feel free to use it. if it isn't they you are are not free without permission unless the renewal was not made. Verifying copyright renewals is a bit arduous, but it can be done.
On a further look it seems that the version on the internet archive linked in the question is a copy of the first edition. It carries a 1917 date, and I see no indication of a revision or 'second edition" or a 1942 date. The IA metadata says "Publication date 1917 " If this is correct, this version and any orall of its contents are in the public domain for anyone to use in any way at all.
Note that if the book had been first published in 1942, the answer would have been different. And the answer would be different again under UK law, which now uses a life+70 term, placing the 1942 edition out of copyright. The same would be true in many other countries which use life+70 or life+50. (The US uses life+70, but only for works published after 1977. The 1978 copyright act came into effect 1 Jan 1978.)
Note that in countries which use a term longer than life+70, and there are a few, this work would not yet be out of copyright.