84 WORMS, INSECTS, AND SHELLS. 



admission; she then fills her abode with atmospherical air, but 

 how I am not able to say. The shell is sometimes found lying 

 at the bottom of the pond, but, rendered buoyant by the air 

 within, it often rises and floats on the surface, and the wily 

 insect is in this manner carried within reach of her prey, who 

 feel no alarm on the approach of what seems a snail ! The 

 stratagem reminds us of the sportsman, who, in some of the 

 fenny counties of England, lies hidden in a shallow boat, and 

 permits himself to be carried by the winds or current amid 

 his unsuspecting game.* 



There is a genus of naked worms (Siphunculus) which 

 makes a similar use of dead molluscous shells. One species, 

 discovered by Mr. Montagu, inhabits old worn specimens of 

 the Strombus pespelicani and Turritella cornea, whose aper- 

 tures it closes with sand cemented by a glairy secretion, 

 leaving only a small circular hole sufficient for the protrusion 

 of its long proboscis, but incapable of admitting any animal 

 by which its safety can be endangered. Another species, 

 common on our northern shores, takes possession of the 

 common tooth-shell (Dentalium entalis), securing the aper- 

 ture in the same manner ; and there are foreign species 

 which exhibit analogous artifices. Other soft worms and 

 zoophytes (Cliona celata) penetrate the substance of shells, 

 boring deep furrows in them, where they safely follow out 

 their life and prescribed duty ; and let it be remembered, 

 that these worms are always constructed with a reference to 

 the shells which they dig into : though the mollusk is inde- 

 pendent of them, they, on the contrary, are entirely dependent 

 on the mollusk. 



There is not the same intimate dependence between some 

 land-shells and some insects that appropriate them ; but the 

 instinct that leads the insects to this appropriation is worth 

 noticing. Two nearly allied to the Bee form their nests in 

 the deserted shells of snails ; one of them (Osmya bicolor) 

 apparently nidifies only in the Helix nemoralis, and the 

 other (Osmya helicicola) most frequently in the Helix poma- 

 tia. Another insect, named Sopyga punctata, inhabits the 

 same shells, and passes its two stages of metamorphoses in 

 the cells of the Osmya. f 



You might think me forgetful were I to conclude this 

 letter without some mention of the Paper Nautilus or Argo- 

 naute, a shell familiar as the ornament of the chimney-piece, 



* I may not find a fitter place than this to mention that the helmet of the 

 frogs, in the War of the Frogs and Mice, is very cleverly shown by Menke 

 to be the Limnaeus stagnalis. Reports on Zoology, p. 417. Lond. 1847. 



t The Naturalist, No. iii. p. 144. 



