ADAPTATION'S 



345 



grubs or larvae of boctlos which hve as "borers" in tree trunks 

 have mere riulinients of legs, or none at all. They have great, 

 strong, l)iting jaws for cutting away the hard wood. They 

 move simply by wriggling jilong in their burrows or tunnels. 



Insects that live in wr.ter either come 

 up to the surface to breathe or take down 

 air underneath their wings, or in some other 

 way, or have gills for breathing the air 

 which is mixed with the water. Tliese gills 

 are special adaptive structures which present 

 a great variety of form and a])i)earance. In 

 the young of the May flies they are delicate 

 platelike flaps projecting from the sides of 

 the body. Tliey are ke])t in constant 

 motion, gently waving back and forth in 

 the water so as to maintain currents to 

 bring fresh water in contact with them. 

 Young mosquitoes do not have gills, but 

 come up to the surface to breathe. The 

 larvae, or wrigglers, breathe through a special 

 tube at the posterior tip of the body, while 

 the pupse have a pair of hornlike tubes on 

 the back of the head end of the body. 



Many fishes, chiefly of the deep seas, 

 develop organs for producing light. These 

 are known as luminous organs, phosphor- 

 escent organs, or photophores. These are 

 independently developed in four entirely 

 unrelated groups of fishes. This difference 

 in origin is accompanied by corres])onding 

 differences in structure. The best known 

 type is found in the Iniomi, including the 



lantern fishes and their many relatives. 



They may have luminous spots, differentiated areas, round or 

 oblong, which shine starlike in the dark. Tliese are usually 

 symmetrically placed on the sides of the Ixxly. They may 

 have also luminous glands or diffuse areas which are luminous, 

 but which do not show tlie specialized structure of the ]>hos- 

 phorescent spots. These glands of similar nature to the spots 

 are mostly on the herd or tail. In oiie gen\is. .^thoprnrn, the 

 luminous snout is compared to the headlight of an engine. 



Fig. 207. — Front leg 

 _of the mole cricket, 

 showing nt e open- 

 ing of uuilitory or- 

 gan. (.\fter Sharp.) 



