Page:The Atlantic Monthly, Volume 18.djvu/148

140 at every stage, and under all conditions. I will merely state very briefly the few facts already established, with some of the possible explanations.

The spinning mammulæ are placed in pairs at the lower part of the abdomen, near its hinder end, and number four, six, or eight in different species. They are little conical or cylindrical papillæ, closely resembling the pro-legs of caterpillars, and are composed of two or three joints, the terminal one of which is pierced with a greater or less number of minute holes, the sides of these, in some, if not all, cases, being prolonged into tubes. Through these holes or tubes issue the fine filaments, which, uniting as they dry in the air, constitute the line from each spinner.

Now the Nephila plumipes possesses at least three pairs of spinners. Of these, two are much larger than the third, which indeed does not appear till they are separated. From the posterior of the two largest pairs seems to proceed the white, and from the anterior the yellow silk, while from the small intermediate pair seem to proceed very fine filaments of a pale-blue color, the use of which is to envelop the prey after it has been seized and killed, being drawn out by the bristles near the tips of the spider's hinder legs. Beside these six papillæ there is, just in front of the anterior pair, a single small papilla on the middle line, the nature and use of which I have not ascertained, though I feel quite sure that no silk comes from it. The large median papilla, just behind the posterior pair, surrounds the termination of the intestines, and through it the excrement is voided, the insect for this purpose turning back the abdomen as she hangs head downward, so that neither the web nor the spinners shall be contaminated. Now it has recently been ascertained that the minute globules with which the circles are studded, and the number of which on a web of average size is estimated at one hundred thousand, do not exist in that form when the viscid lines are first spun by the spider, but as a uniform coating of gum upon a thread; this gum, of itself and according to physical laws, soon exhibits little undulations, and then separates into the globules which have long been observed and supposed to be formed by the spider. The fact of spiders selecting the night for the construction of their webs, the difficulty of making any close observations upon them while so engaged without disturbing them, and the near approximation of the two larger pairs of spinners while the viscid line is slowly drawn out by the hind leg, have hitherto prevented my determining its exact source and manner of formation. If it comes from the anterior pair only, then one and the same organ has the power of evolving a central axis and covering it with viscid gum; and it seems less improbable that the axis is white and formed by the posterior pair, the yellow gum being spread upon it by the anterior pair, which also would then have the power to evolve this same gum at other times as an equally dry, though more elastic thread. But in either case we have only three pairs of spinners and four kinds of silk, the pale-blue fasciculi the dry white, the dry yellow, and the viscid and very elastic silk which is employed only in the circles of the web, and which often does not become yellow till after exposure to the light. Apparently the surest method of investigation will be carefully to destroy one pair of spinners at a time without injuring the others, and then note the effect upon the spinning.

Let us go back now to the sixty spiders left at Mt. Pleasant. A few of these died on the way North, but the majority reached Boston in safety about the 20th of September, 1865;