82 Cincinnati Society of Natural History. 



the bottom singly, while others are held together by strips and 

 bands or masses of adhesive or glutinous material, by which they 

 become attached to plants, sticks or pebbles, or float on or 

 near the surface, and still others are carried about by the male 

 fish in various places or receptacles of its body until they are 

 hatched. 



Not only do the ova of fishes differ very much in appearance, 

 b)ut there exists a great diversity in their size, and consequently in 

 the number of eggs produced by the different species — thus in a 

 marine catfish the ova are as large as robin eggs ; in the salmon 

 they are one-fourth of an inch, and in the brook trout three-six- 

 teenths of an inch in diameter ; in one of the gars they are, with 

 their envelope, a fourth of an inch in diameter, while in the eel 

 they are almost microscopic. 



The number of eggs produced by a female fish varies according 

 to its age and weight. In several species of familiar fishes the 

 number of their eggs have been ascertained by careful and accurate 

 calculations to be as follows: In the marine catfish (^G. felis), 

 from lo to 30 eggs; brook trout, from 100 to 1,800; salmon, 

 5,000 to 15,000; black bass, 5,000 to 20,000; lake trout, average, 

 15,000; sea herring, 10,000 to 30,000; shad, 25,000 to 100,000; 

 white fish, 20,000 to 70,000; pike, average, 100,000; mackerel, 

 300,000 to 500,000; Spanish mackerel, 300,000 to 1,500,000; 

 halibut, 2,000,000; striped bass, 2,000,000; carp, average, 

 500,000; sturgeon, as many as 7,000,000; Cod, 9,000,000, while 

 in the eel there are also several millions. 



It has not been many years since all fishes were supposed to 

 deposit their spawn upon the shoals of the sea-shores or upon the 

 beds of shallow inland streams, where the ova rested until hatched; 

 but we now know that many marine species deposit their eggs at 

 the surface of the ocean, where they float until incubation is 

 complete. 



In 1864, Prof. G. O. Sars, of Norway, first discovered that the 

 eggs of the cod floated at the surface. Since then the investigations 

 of Prof. Alexander Agassiz and Mr. John A. Ryder have added 

 largely to our knowledge of floating eggs. Mr. Ryder character- 

 izes several types of buoyant ova: i. Those in which the specific 

 gravity of the yolk is diminished, as in the egg of the cod ; 

 2. Those in which large oil-drops, in an eccentric position, aid in 

 causing the eggs to float; 3. Those in which a very large oil- 

 drop causes the ovum to float even in fresh water. The other 



