Page:Popular Science Monthly Volume 6.djvu/673

Rh .—In these clays of evolution, we can hardly wait to learn what an animal does in the present, before we inquire what its ancestors were, and how it came to be what it is.

Ideally, one may at once draw a curious comparison between Hyptiotes and two other spiders already referred to in this article, namely, the Epeira and the Nephila for the net of the former is a complete circle, that of the latter is a circle lacking its upper sextant, while the net of Hyptiotes is just about the sextant or sixth of a circle. To use a more homely comparison, the net of Epeira is an entire pie, that of Nephila is a pie with a piece cut out, while that of Hyptiotes represents the missing piece. In algebraic language, Nephila $$+$$ Hyptiotes $$=$$ Epeira.



But, while the above comparison enables us to contrast the nets of the three genera, it by no means satisfies the inquirer as to the derivation of the forms in question. To answer this in full would require a more complete knowledge than we now possess, and would involve a discussion too technical for these pages; but there are a few considerations easily presented, which indicate that the gaps between the forms are not so great as at first appears.

1. The net of the ordinary geometrical spiders, like that of Epeira riparia, consists of a continuous spiral viscid line laid upon radii, while that of Nephila presents a larger number of radii upon which is laid a looped viscid line, which does not extend across that part of the circle just above the centre. But in several nets, otherwise of usual geometrical character, I have found one or the other side, but usually the bottom, extended considerably by the addition of several looped lines, like those made by Nephila; so that we may imagine that Nephila has merely perpetuated and intensified into constancy a method of net-making which was occasionally employed by the form from which it and the common Epeira are both descended.

2. At least one species of Epeira (the E. calophylla of Great Britain, described by Mr. Blackwall) constructs a net of looped lines, like that of Nephila, but the loops terminate on both sides of a single radius, which serves as a line of communication between the centre of the net and a cell under a neighboring leaf. Now, if we imagine the net to be reduced from many radii to four, then the single divergent radius of E. calophylla would represent the apex-line of Hyptiotes.

3. Many and perhaps all geometrical spiders are accustomed to shake their nets violently when touched, and sometimes to seize