BODILY CHARACTERISTICS INCONSPICUOUSNESS 279 



(Ctenophora). Transparency or translucency is a highly char- 

 acteristic feature in hosts of the free -swimming young which 

 belong to such groups as Molluscs, unsegmented and segmented 

 Worms, Lamp- Shells, Moss- Polyps, Crustacea, and Echinoderms. 

 A typical instance is that of the little Glass -Crabs which were 

 originally believed to be distinct species, but are now known to 

 be the larvae of Rock- Lobsters (Palinurus] and related animals. 



SNOW ANIMALS. Another striking and well-known instance 

 of general resemblance to surroundings is afforded by snow and 

 ice animals, which by possession of white fur or feathers are 

 rendered extremely inconspicuous. Mammals and Birds furnish 

 a number of striking examples. It is a rare occurrence for an 

 animal to be white all the year round, for this can only be ex- 

 pected to happen in very high latitudes, where the ground is 

 permanently covered by snow and ice. The Polar Bear is an 

 instance, but the colour in this case is almost entirely aggressive, 

 enabling the animal to approach its prey without attracting 

 observation. 



Among birds the Snowy Owl (Nyctea Scandiacd] of the Arctic 

 regions, but which sometimes wanders into more southern lati- 

 tudes, as e.g., North Scotland, is permanently coloured so as to 

 harmonize with snowy surroundings. Its prevailing hue is white, 

 but this may be flecked or barred with blackish-brown. Though 

 in the main aggressive in purpose, the Owl is doubtless protected 

 to some extent by its resemblance to the background against 

 which it is usually seen in the far north. 



DESERT ANIMALS. Many animals which inhabit desert regions 

 exhibit general protective resemblance to their surroundings, 

 exemplifying in a practical manner the value of khaki tints 

 where concealment is desirable. The colour is by no means 

 always of uniform character, for there may be spots, flecks, or 

 stripes, all being calculated to make assimilation with the sur- 

 roundings more complete. Camels, Antelopes, Desert Foxes 

 (fennecs), and Jerboas are good instances among the Mammals, 

 while ancestral Horses were probably clad in striped khaki. 

 Among birds may be mentioned Desert Larks, Desert Finches, 

 and Sand-Grouse (fig. 474). Of the last, Brehm (in From North 

 Pole to Equator] writes graphically as follows, in reference to the 

 Sahara: "Among the sparsely sprouting alfa there is a numerous 

 flock of birds about the size of pigeons. Tripping hither and 



