500 BULLETIN 188, UNITED STATES NATIONAL MUSEUM 



water. * * * The beach-skippers or mud-skippers, though they do not wander 

 far from water, have eyes well adapted for vision in air. In this respect they 

 are better adjusted to land life than species, such as the climbing-perch (AnaMs 

 testudineus) , which often make long journeys overland but nevertheless have 

 eyes adapted for seeing in water. * * * Their eyes are better suited for 

 distant perception than those of fishes which are active in water. The fins and 

 tails of beach-skippers are also adjusted to locomotion in air. An active goby 

 can progress much faster than a man over a mud fiat. The skins of such fishes 

 are thicker than those of aquatic gobies and thus conserve water. * * * The 

 respiratory organs show anatomical and physiological adaptations for breathing 

 in air. * * * 



Four species were studied in some detail * * * Periophthalmus koelreuteri 

 (Pallas), Periophthalmodon sclilosseri (Pallas), Boleophthalmus ioddaerti 

 (Pallas), and Glossogohius giuris (Hamilton). 



The first three species lived on the mud flats, the third usually somewhat 

 lower down than the first and second, but all three went up and down together 

 with the tides and even invaded the zone above high-tide mark, where they hunted 

 for food among mangrove roots and hydrophytic plants. The first species was a 

 strictly aquatic goby, which never came out of the water. In Java, Harms * * * 

 found beach gobies arranged in more or less definite zones. This was not 

 true of the three common species at Paknam, which continually mingled to- 

 gether. Though these fishes lived together, they were not competing to any 

 extent. They were different in size, food, length of intestine, and type of 

 parasites. * * * 



The long-intestined, vegetarian Boleophthalmus was the only fish which har- 

 bored intestinal flagellates. This agrees with the observation of Hegner * * " 

 on the relation of diet to flagellate infestation in mammals. Tapeworm and 

 acanthocephalan cysts were present only in the largest land gobies. Adult 

 nematodes, tapeworms, trematodes, acanthocephalans, copepods, and Spmitecttis 

 cysts were found only in the aquatic goby. * * * Agamofilaria cysts occurred 

 in the carnivorous land gobies. Parasitic isopods * * * were often en- 

 countered on ti>e gills of all the gobies, but were most abundant on the aquatic 

 species. The largest land goby [Boleophthalmus] was most often infested with 

 parasites; hut the largest number of parasites per individual and the largest 

 number of species of parasites occurred on the aquatic goby. Perhaps the 

 former was more often infested because it visited a greater variety of habitats ; 

 perhaps tlie latter contained more parasites per individual because it lived 

 continually in water and was thus susceptible at all times to aquatic parasites. 

 By taking up land life, gobies appear to have escaped from certain types of 

 parasites. 



Land gobies have also attained other desiderata by becoming terrestrial. They 

 move faster in air than in water and can thus, with their peculiarly adapted eyes 

 and limbs, seek food and escape enemies better than their aquatic relatives. 

 They probably escape some aquatic enemies besides parasites when they leave 

 the water. They also encounter new dangers in the way of astute enemies and 

 parasites. For example, the Agamofilaria cysts which occur in land gobies 

 probably come to maturity in fish-eating birds or naammals. 



When a fish changes from an aquatic to a terrestrial mode of existence, pro- 

 found changes in its anatomy and physiology must take place. These must, in 

 such a highly organized animal as a fish, be accompanied by modifications in the 

 nervous system. * * * During past ages aquatic vertebrates undoubtedly 

 gave rise to land vertebrates. It appears probable that many aquatic types were 

 able to breathe air before they attained land life, probably as an adaptation to 

 lack of oxygen in shallow, stagnant bodies of water. * * * 



