33° 



FRESH FACTS [april 1899 



Bird-Catching Spiders. R. I. Pocock. " The Genus Poecilotheria : Its 

 Habits, History, and Species," Ann. Nat. Hist. iii. 1899, pp. 82-96, 1 pi. 

 This genus is a representative of that great and almost cosmopolitan group of 

 spiders which was formerly included under the comprehensive title Mygale, 

 which still persists in many books. The observations of Madame Merian and 

 Mr. Bates have formed the slender foundation for the widespread and 

 sensational belief that the staple article of food of these spiders consists of 

 small birds. " As a matter of fact, there is no doubt that they feed almost 

 entirely upon insects ; but they will certainly also kill and devour any living 

 animal they are powerful enough to overcome. The species of Poecilotheria are 

 tree-living forms, and their colouring is adapted on the upper surface for 

 protective concealment on bark overgrown with lichen and moss. The colour 

 of the under side is startlingly different, is exposed when they rear themselves 

 on their hind legs, and is probably of warning significance. They also possess 

 a stridulating organ between the mandible and the palp. Eight species are 

 described from Ceylon and S. India." 



Selective Action of Frost. T. D. A. Cockerell. " Vernal Phenomena 

 in the Arid Region," Amer. Naturalist, xxxiii. 1899, pp. 39-43. From 

 observations on plants and bees made by himself and other workers at the 

 Mesilla Park Experiment Station, New Mexico (altitude 3800 feet), Prof. 

 Cockerell concludes that "throughout the arid region, where the sky is clear 

 and the radiation great, the development of plants and insects is controlled 

 largely by the distribution of frosts throughout the year. In the course of 

 natural selection the native species (except such as are frost-proof) have learned 

 not to appear or develop until the clanger of frost is over." There is warmth 

 enough, as is shown by the behaviour of introduced fruit-trees which rush into 

 bloom and get nipped. The horticulturist's device must be to select late 

 varieties which will escape the frosts. 



Dimorphism. E. G. Conklin. " Environmental and Sexual Dimorphism 

 in Crepidula," Proc. Ac. Nat. Sci. Philadelphia, 1898, pp. 435-444, 3 pis. 

 In various species of this genus of sedentary gasteropods there is " environmental 

 polymorphism," i.e. the form and colour differ according to the nature of the 

 shells on which the animals live. In Crepidula plana there are dwarf and 

 giant forms, and the difference in size is associated with a difference in the 

 number, not in the size, of the component cells. The dwarfing is a " modifica- 

 tion " and not inheritable. In the same species sexual dimorphism is also well 

 marked, the average female being about fifteen times the size of the male. 



Detection of a Robber Ant. E. Wasmann. " Lasius fuliginosus als 

 Raubameise," Zool. Anzeig. xxii. 1899, pp. 85-87. This glossy black wood-ant, 

 which finds its usual food-supply in aphides, has not hitherto been known as 

 a robber. But Wasmann has detected it in the act of plundering the nest of 

 Myrmica laevinodis and carrying off the larvae and pupae. The observer does 

 not believe, however, that we have here any hint as to the origin of a mixed 

 colony. The captives are simply devoured. 



