Phthinobranchii 229 



and at the same time they devour the eggs of all species acces- 

 sible to them. In almost all fresh and brackish waters of the 

 north temperate zone these little fishes abound. "It is scarcely 

 to be conceived," Dr. Gunther observes, "what damage these 

 little fishes do, and how greatly detrimental they are to the 

 increase of all the fishes among which they live, for it is with 

 the utmost industry, sagacity, and greediness that they seek 

 out and destroy all the young fry that come their way." 



The sticklebacks inhabit brackish and fresh waters of the 

 northern hemisphere, species essentially alike being found 

 throughout northern Europe, Asia, and America. The same 

 species is subject to great variation. The degree of develop- 

 ment of spines and bony plates is greatest in individuals living 

 in the sea and least in clear streams of the interior. Each of 

 the mailed species has its series of half -mailed or even naked 

 varieties found in the fresh waters. This is true in Europe, 

 New England, California, and Japan. The farther the indi- 

 viduals are from the sea, the less perfect is their armature. 

 Thus, Gasterosteus cataphractus, which in the sea has a full 

 armature of bony plates on the side, about 30 in number, will 

 have in river mouths from 6 to 20 plates and in strictly fresh 

 water only 2 or 3 or even none at all. 



The sticklebacks have been noted for their nest-building 

 habits. The male performs this operation, and he is provided 

 with a special gland for secretion of the necessary cement. 

 Dr. Gill quotes from Dr. John A. Ryder an account of this 

 process. The secretory gland is a "large vesicle filled with a 

 clear secretion which coagulates into threads upon contact 

 with water. It appears to open directly in front of the vent. 

 As soon as it is ruptured, it loses its transparency, and what- 

 ever secretion escapes becomes whitish after being in contact 

 with water for a short time. This has the same tough, elastic 

 qualities as when spun by the animal itself, and is also composed 

 of numerous fibers, as when a portion is taken that has been 

 recently spun upon the nest. Thus provided, when the nuptial 

 season has arrived the male stickleback prepares to build 

 his nest, wherein his mate may deposit her eggs. How this 

 nest is built, and the subsequent proceedings of the stickle- 

 backs, have been told us in a graphic manner by Mr. John K. 



