284 Dr. F. Plateau on Argyroncta acjuatica. 



extremities of these rudiments of palpi and legs thus finally 

 cross upon the median line. The transverse projections^ there- 

 fore; do not, as has sometimes been asserted, produce the limbs 

 by dividing in the middle; but the limbs, in the Araneida, 

 seem to have an independent origin. 



I shall pass over some observations relating to the habits of 

 the young animals after hatching, and come to the second part 

 of my memoir, in which I deal with the adult Argyroneta. 



The nest in which the Argyroneta deposits its eggs has long 

 been known ; but I have ascertained that the animal constructs 

 for itself another kind of dwelling, in which it resides ha- 

 bitually. This is a spherical or ovoid cell, with delicate, almost 

 transparent walls, presenting only a small opening at the bottom. 

 Instead of being situated at the surface of the water like the 

 nest, it is placed at a considerable distance from the surface, 

 and concealed by masses of aquatic vegetation, in which the 

 animal hollows out a small cylindrical horizontal canal, making 

 a communication from the aperture of the cell into the sur- 

 rounding water ; at least this is what I observed when the ha- 

 bitation was constructed by an Arg^jroneta in captivity in a 

 glass vessel. 



According to De Lignac, Clerck, and those who have copied 

 them, the spider first of all completely builds its cell, and then 

 fills it with air. According to my observations this is not quite 

 correct ; and the following is what I have ascertained with re- 

 gard to the submerged dwelling (two of the Argyronetm that I 

 kept in captivity having by chance commenced their cells be- 

 tween the aquatic plants and the glass wall of their bottle) : — 

 The first steps of the construction are difficult of observation ; 

 but we may conclude, from the sort of dragging undergone by 

 the Algse and Confervse, that the animal commences by fixing to 

 these plants a comparatively small number of threads arranged 

 so as to intercross nearly at the same point. The tenuity of 

 the threads and their immersion in the water render the net- 

 work at first invisible; but it soon betrays itself in the follow- 

 ing manner : — the Argyroneta comes to the surface to procure 

 a certain quantity of air, which it throws off under the net- 

 work of which we have just spoken ; in consequence of its 

 lightness the air ascends in the form of a bubble, and meeting 

 the threads adheres to them and pushes them upwards, giving 

 them the form of a little dome. From this moment the imprison- 

 ment of the bubble of air, the increase of the dragging by which 

 the algse are aff'ected, and, finally, other threads which the 

 Argyroneta successively adds to the meshes surrounding the 

 bubble leave no longer any doubt as to the existence of the 

 network, which we even begin to see. Fresh quantities of 



