414 MIMICRY IN SPIDERS. 



generally remove them. Balsam-mounted objects require no ring 

 of cement to retain the covers in position, but the application of 

 one or two coats of Bell's cement will prevent the cedar-wood oil, 

 used with immersion objectives, dissolving out the balsam at the 

 edge of the covers. Further details of processes and full particu- 

 lars regarding the various solutions, cements, etc., will be found in 

 Lee's ' Microtomist's Vade Mecum,' and Squire's ' Methods and 

 Formulae.' 



flDimicr^ in Spibere* 



MIMICRY is one of the subjects which most secure the 

 attention of the general public in natural history, and one 

 which working naturalists are very apt to notice. No 

 person in any degree, accustomed to take notice of animals and 

 plants, has failed to observe cases of mimicry, whether on the sea- 

 shore, in the forest, or on the prairie : and with the advances of 

 observation we see, in fact, that protective colouration and mimicry 

 are most abundant in nature. 



One recent case has been quoted by a French botanist, 

 Professor Heckel, of Marseilles. It concerns a species of spider, 

 Thomisus onustus^ which is frequently met with in France, where 

 it commonly— at least in the South of France — lives on the com- 

 mon Convolvulus arvensis^ being very partial to two diptera, 

 No7niodes minutissimus and Melithreptus origane^ which are frequent 

 visitors to this flower. Professor Heckel has noticed that Convol- 

 vulus is met under the slightly differently coloured varieties ; one 

 is quite white; the second is pink, of a light tint, with some parts 

 of deeper colour; the third is also of a light pink, with some green 

 on the external side. These three varieties are quite common, and 

 live side by side. Now the curious fact is that each of these three 

 forms affords lodgings to three corresponding varieties of Thojuisus 

 onustus. In the white flowers is found a variety which is white 

 with a little blue cross on the back. In the flowers, which are 

 greenish externally, we find a Thomisus which is also greenish, with 

 some pink, and this form lives on the flowers, not in it like the two 



