260 MR. K. I. POCOCK — MIMICRY IN SPIDERS. 



groups. Instances, however, are not unknown amongst species o£ the latter 

 kind. 



In the Argyopidse the males o£ the tropical American genus Micratliena 

 {Acrosoma) differ strikingly from the large, gaudily (warningly) coloured, 

 spiny females in having the abdomen black, slender^ oval and elongated. In the 

 males of Ildihalia mutilloides (PL 32. fig. 1) and myrmicceformh, belonging to 

 a genus closely allied to Micratliena, the abdomen is smooth, unarmed, deeply 

 constricted in the middle, globular behind and oval in front of the constriction, 

 where it meets the carapace which is itself narrowed behind. In an allied 

 species, /. albomaculata, the abdomen is simply oval and without constriction. 

 In butterflies it is common for the females alone to mimic a protected model, 

 because being larger and heavier than the males and compelled to alight and 

 remain at rest during oviposition, \hej are exposed to greater dangers of 

 capture. This is reversed in the case of the spiders above mentiwied. The 

 females have a protective armature of spines and live in webs from which 

 they can drop at once into the herbage beneath and lie absolutely still, 

 hidden from the enemy that has startled them. But the males are not only 

 without the spiny armature^ but are compelled by the pairing instinct to 

 wander about in search of the webs of the females. Another spider of this 

 family, namely Melyciopharis ci/nips/is said by Simon to resemble ants. The 

 thorax is attenuated behind, the waist is strongly pronounced, and the abdomen 

 is globular. It is a native of the Amazons. 



Formicina, one of the Linyphiidse, a group which should probably be 

 united with the Argyopida?, has the carapace very narrow and long behind 

 and the cephalic region high and shining ; the abdomen is globular but not 

 coriaceous, and the legs are long and slender. The spider lives on the 

 ground and spins a large horizontal web amongst grasses or other low 

 herbage. It occurs in South Europe and has a nearly related aWj (Solenysa) 

 in Japan. Both are ant-like. 



The Theridiidge furnish a few examples of this phenomenon, all met with in 

 South America. Formiciiioides has the carapace long, low, and produced far 

 beyond the posterior legs in the form of a narrow cylinder where it passes 

 into a short pedicel or waist connecting it with the abdomen, which is high. 

 Cerodida much resembles the foregoing, but has the abdomen short and 

 globular. In Audifia the carapace is also long, oval, and narrowed behind, 

 but does not surpass the posterior coxfe ; the abdomen is globular, with a 

 hard shininf^ smooth inteo-ument. 



Coming now to the sedentary species, the Eresidse furnish an instance 

 analogous to that of Ildihalia mentioned above. In most species of this 

 family the secondary sexual characters are well marked, especially as regards 

 colour. But only in the case of the South-African genus Seothyra has an 

 explanation of the difference been offered. The females of this spider 

 (Seothyra schreinen) live in burrows in sandy parts of the veldt. The 



