744 



ZOOLOGICAL SOCIETY BULLETIN. 



t; 



FULLY DEVELOPED I t I 



cies. The two species are so similar in nearly 

 every respect that they would naturally be sup- 

 posed to have the same breeding habits. 



The distribution of the eel on both sides of 

 the Atlantic has been carefully studied by Dr. 

 Schmidt. Only one species is known on each 

 side of the Atlantic, and these are apparently 

 kept apart by the greater depths of the middle 

 Atlantic. Not only are the inland waters of both 

 continents penetrated by the eels, but they are 

 also found in the fresh water streams of the 

 oceanic islands, such as the Bermudas and 

 Azores, from the tropics nortliward to Iceland, 

 even in islands where no other fresh-water fishes 

 exist. Tile F.uro])ean species occurs from North 

 Cape soutliward to the coast of Morocco in Af- 

 rica and througliout the tributaries of the Baltic 

 and IMediterranean Seas. It is not found in the 

 Black Sea nor its tributary streams. Our Amer- 

 ican species is distributed from I^abrador and 

 the southern end of Greenland to Guiana, but is 

 rare along the southern coast of the Caribbean 

 Sea. 



It will be noticed that the eel reverses the 

 breeding migration of the salmon, shad and other 

 well-known fishes that breed in fresh and shal- 

 low waters, while their young return to the ocean 

 lor their growth period. Their peculiar habits 

 make it impossible to propagate them by artifi- 

 cial methods or to establisli them in other re- 

 gions of the world where the special conditions 

 of the breeding grounds do not exist. The 

 young eels can be readily transported and will 

 grow well in fresh water anywhere, but attempts 

 to establish the American eel on the Pacific coast, 

 have met with no results beyond the growth of 

 the individuals transported, and the same has 

 been true of the attempt to plant the European 

 eel in the Danube and other tributaries of the 

 Black Sea. R. C. O. 



SKATES AND 



FLOUNDERS. 



A STl'DV IN ADAPTATION. 



WO groups of our 

 local fishes that are 

 very highly adapted 

 to life on the sea bottom 

 arc the flounders and the 

 skates. While these 

 groups are about as wide- 

 ly separated in their re- 

 lationships- as fishes can 

 be, they have botli been able to solve very suc- 

 cessfully the problem of adaptation to similar 

 conditions. However, they have been compelled 

 to do this in very different ways, for the skates 

 are relatives of the sharks and have undergone 

 a process of evolution in whicli the rounded body 

 of the shark lias assumed a greatly depressed or 

 flattened form, while the flounder is a bony fish 

 with a body greatly compressed from side to 

 side. Its ancestors swam after the ordinary 

 manner of fishes, but in order to adapt them- 

 selves to the bottom were comiielled to lie on one 

 side. Any similarities of form or habit between 

 the flounders and skates must therefore be mere- 

 ly cases of resemblances ])roduced in the attempt 

 to suit themselves to the same conditions of life. 

 Tlie changes tliat liave come about in these fishes 

 during this process of adaptation are worthy of 

 our consideration. 



The skates or rays (sub-order Batoidei or 

 Rajida), are a modified offshoot of the sharks, 

 (Elasviobranchii) , that have assumed a life on 

 the sea floor instead of swimming in its upper 

 waters like their relatives. Their food, for the 

 most parL, consists of those animals which are 

 either sessile or move but slowly, and in most 

 cases their teeth are adapted to crushing the 

 shells of molluscs and other animals with ex- 

 ternal skeletons. 



WHien we examine a skate we find a thin disc- 

 like body witli a broad head, very broad lateral 

 fins, and a long, slender tail, which in some cases 

 is so narrow and long that it forms a whip-like 

 member. Viewed from the under side the head 

 shows a number of peculiarities. As the food 

 is obtained on the bottom the mouth is on the 

 underside of tlie head so that the food may be 

 obtained without changing the position of the 

 body more than is necessary to bring the mouth 

 over the food. The nostrils also are placed well 



