BULLETIN OF THE UNITED STATES FISH COMMISSION. 193 



The nature and origin of the material by which adherent ova are 

 made to stick fast to foreign bodies and to each other is an interesting 

 inquiry. It appears to be a mucous substance, derived, possibly, as a 

 peculiar secretion either from the ovarian follicles or some special gland- 

 ular structures within the ovary. Its remarkable property of harden- 

 ing under water I find to be characteristic of the material in all the 

 species with adhesive ova which I have yet had the opportunity of ex- 

 amining. 



VIII. — NOTES ON SMALL FISHES AND WATER ANIMALS WHICH PREY 



ON FISH LARV^). 



Eecently (June 1882) some four-spined sticklebacks (Apeltes quadra- 

 cus) in spawning condition were received at the Central or Armory 

 hatching station of the United States Fish Commission from Mr. W. P. 

 Seal, of Philadelphia, who, in his letter announcing their shipment, in- 

 formed me that they would not accept dead food, but must be supplied 

 with small living insect or crustacean prey, which they would themselves 

 capture. The specimens were mostly males, and would measure an inch 

 and three-eighths in length ; some were smaller. Mr. Seal's opinion as 

 to their feeding habits was soon verified, as it was found that dead food 

 had not the slightest attraction for them, but as soon as live food was 

 offered them they exhibited a vivacity and alertness in its capture which 

 was truly surprising. I obtained a supply of this from the government 

 carp ponds by skimming the surface of the water amongst a rank growth 

 of aquatic plants with a fine net, where it was found that DapMniidw, 

 neuropterous, and coleopterous larvae abounded, as well as numerous 

 brown aphides, which had blown on to the surface of the water from the 

 taller plants fringing the pond. These creatures were transferred to 

 the aquarium containing the sticklebacks, when the work of destruction 

 was at once commenced. The lively little ichthian marauders would 

 poise themselves in the water, roll their eyes, and when one of their vic- 

 tims was within sure range they would pounce upon it, rarely missing 

 their mark, in spite of the fact that the latter, as in the case of the Daphnids, 

 might happen to be quite minute. Hard-shelled coleoptera and bugs 

 were not accepted, nor did the larger neuroptera seem to attract their 

 serious attention. The smaller, softer-bodied animals seemed to be most 

 palatable. Upon observing this, it occurred to me to try them upon 

 shad larvae. About twenty-five of these, three days old, were then put 

 into the jar ; no sooner than they had made themselves conspicuous by 

 their active wriggling movements through the water, the keen eyes of 

 the sticklebacks perceived them; their destruction was completed in 

 about half an hour by the half-dozen individuals of Apeltes. The experi- 

 ment was repeated with a similar result, showing the destructive capac- 

 ities of Apeltes when brought to bear upon helpless shad larvae. Gunther 

 has noticed the voracity of Gasterosteus in his " Study of Fishes." 



It has been maintained by some writers that fish larvae, which in the 

 Bull. U. S. F. C, 82-1-13 March 14, 18 83. 



