68 MIMICRY 



and is aptly named Psyche helix, a kindred species from Italy 

 being known as Ps. planorhis. 



An insect larva ( Cochlophora valvata) from E. Africa is said 

 to resemble a Valvata or young Cyclostoma. In this case the 

 spiral is indifferently dextral or sinistral, the ' shell ' being 

 formed of masticated vegetable matter, united together by 

 threads spun by the larva. Certain larvae of the Phryganeidae 

 (" Caddis-worms ") enclose themselves in houses which more or 

 less resemble a spiral shell, and have in some cases actually been 

 described as moUuscan; such species, some of which belong to 

 Helicopsyehe, have been noticed in S. Europe, Ceylon, Further 

 India, China, Tasmania, New Zealand, Tennessee, Mexico, Cen- 

 tral America, Venezuela, Brazil, and Argentina, and alP possess 

 a dextral ' shell.' In all these cases ' mimicry ' is probably not 

 so much to be thought of as the practical advantages which 

 accrue to the animal in question from the spiral form, which 

 gives it greater strength to resist external blows, and enables it 

 to occupy, during a very defenceless portion of its existence, a 

 very small amount of space. 



The larva of some species of the Syrphidae QDiptera) fixes 

 itself on the under side of stones in the Tyrol, and closely 

 resembles a small slug. The naturalist Von Spix, in 1825, 

 described to the Bavarian Academy as a new genus of land Mol- 

 lusca a somewhat similar larval form found in decaying wood 

 on the banks of a German lake.^ Simroth mentions ^ a curious 

 case as occurring near Grimma. The caterpillars of certain 

 Microlepidoptera occur on slabs of porphyry, associated with a 

 species of Clausilia. Besides being of the same colour as the 

 Clausiliae, the caterpillars have actually developed cross lines 

 on the back, i.e. on the side turned away from the rock, in imi- 

 tation of the suture of the mollusc. 



It has been suggested * that there is mimicry between Aeolis 

 papulosa (a common British nudibranch) and Sagartia troglo- 

 dytes (an Actinian), and also between another species of 

 Sagartia and Aeolidiella Alderi. The facts observed are not 

 sufficient to warrant a decided opinion, but it seems more proba- 



1 Von Martens, SB. Nat. Fr. Berl. 1891, p. 83. 



2 Von Martens, ibid. 1887, p. 183. 3 g^. Nat. Gesell. Leipz. xiii.-xiv. p. 45. 

 "* Carstang, Journ. Mar. Biol. Ass. N. S. i. p. 432 ; Giard, Bull. Sci. Fr. 



Bel(j. 1888, p. 502 f. 



