106 



NATURAL HISTORY OF ARTHROPODS. 



In most species these differences are not great ; but in some no one would ever suppose, 



without other evidence, that the males and females had any relationship to each other. 



The most extreme cases of this kind are Argiope and Nephila, where the male is about 

 a tenth as long as the female. 



In the genus Erlgone, which includes the smallest known spiders, 

 the males often have curious humps and horns on their heads. The 

 most extreme example is shown in Fig. 146, where the eyes are car- 

 ried up on the end of the horn. The females of all these species have 



FIG. 146. Head of plain round heads ; and what use the humps are to the males nobody 



Erlgone. J 



knows. 



The peculiar organs by which the adult males and females can always be dis- 

 tinguished are, in the males, the palpal organs, on the ends of the palpi ; and, in the 

 females, the epigynum. 



As the male spider gets nearly full grown the terminal joints of the palpi be- 

 come swollen, and, after the last moult, the palpal organs are 

 uncovered. The simplest form of palpal organ is found in 

 the large Mygalida?. It consists of a hard bulb, drawn out 

 to a point, in which is a small hole leading to a sac within. 

 In most spiders the terminal joint is flattened, and lias a hollow 

 on the under side, in which the palpal organ is partly concealed. 

 The bulb is flattened to fit this hollow, and the point of it is pro- 

 longed into a distinct tube of various shapes furnished with num- 

 erous spines and appendages. In Tlieridion the outer tube is so 

 long that it is coiled up over the basal part of the bulb, and the 

 end rests on a strong spine at one side of the palpus. The shape 

 of these organs is very constant in the same species of spider, and 

 thus they afford good characters in distinguishing species. 



When the female spider is nearlv full grown there appears a FIG. 147. Palpal organ 



. of Theridion. 



hard, swollen place just in iront ot the opening ot the ovaries, 



and after the last moult the epigynum is uncovered 

 at this place. The epigynum consists of two sacs 

 or spermathecae, which connect by two little tubes 

 with the oviduct near its mouth, and by two larger 

 tubes with the outside of the spider. The mouths 

 of these larger tubes are often surrounded by vari- 

 ous hard appendages. These parts, like the palpal 

 organs, furnish convenient marks for distinguishing 

 species. The spermathecae vary but little in shape 



FIG. 148. -Epigynum of Theridion. E.Sper- in different spiders, but the tubes are often length- 

 S a Tubes ofen?ng b outward ng tO oviduct ' ened and twisted into shapes nearly as complicated 



as those of the palpal organs. Thus in the epigy- 

 num of some species of Theridion the larger tubes are very much elongated and 

 twisted up, corresponding to the long discharge-tube of the palpal organ of the male 

 of the same spider. 



When the reproductive organs of the male spider are mature he discharges the liquid 

 contained in them on a little web spun for the purpose ; dips his palpal organs into it, 

 and in a few moments takes up the whole into the little sacs inside the bulb ; then he 

 seeks the female, and inserts the palpal organs into her epigynum. The soft part at 



