500 PARENTAL CARE AMONG FRESH-WATER FISHES. 



Indeed this iipiieoraiice is .-issuiiied while the seoretiou is contained in tiie 

 nveters. The epithelial cells of the iii-inai-y c-anals exert so actively the secret- 

 ing function that the bladder becomes nmch distended by the accunuilating 

 mucus, and at length it tlows slowly to the urinary aperture, where it emerges 

 as a tenacious elastic thread which readily adheres to any external object on 

 contact. It can hardly be doubted that this secretion can be extruded at 

 pleasure, the walls of the bladder, assisted by the abdominal parietes, being 

 sufficient to effect this ; but it is produced so abundantly that it also often 

 appears to ooze out involuntarily. Male fishes may often be seen with a glisten- 

 ing, pendulous, conoid mass hanging from the urinary aperture, and increasing 

 in size until it liecomes detached. Such tiask-shaped masses of mucus occur 

 frequently in tanks where these fishes f.re confined and no opportunity is 

 afforded for nest building. When, however, an appropriate mass of seaweeds 

 has been selected by the male, the fish has merely to approach closely, so that 

 the protruding mucus may adhere to a projecting frond, and by passing and 

 repassing round the mass the weaving operation is accomplished. Occasionally 

 ;\ rapid ejaculatory movement is observed, and it is interesting to note that the 

 threads are not carelessly sujierposed, except when necessary for increasing the 

 density of the nest, but are crossed at an angle by the varying movements of 

 the fish, so that rhomlioidal si»aces are inchtsed and a i-egular i-cticulum is tiuis 

 produced ( ]>1. i, tig. r> ). 



Often the tightly d>-awn thread snai>s asunder, though its tenacity is extreme. 

 The fibers then curl up and form a terminal pellet, many of which occur on the 

 surface of the nest. As before remarked, the nmcus is not merely a semisolid 

 plasm, but jissumes a funicular character while in tlu' ureters. If one of the 

 chords binding a nest together be examined, it will lie foniid to consist of several 

 strands, the cord itself measuring from (».()()4(> to O.dO."*! inch in diameter, and 

 the constituent threads from (».0()08 to 0.()()(»!>2 inch. These smaller threads 

 again consist of fine homogeneous filaments, which adhere in parallel order. 

 The parallel arrangement of the ultimate fibrils is very striking .and quite char- 

 acteristic ( ]il. I. fig. 41. 



The stickleback is hy no means a nioiiogamist, as was once believed, 

 but endeavors to induce a numlier of females to deposit eggs in the 

 nest he has built. His bellicose tendency, always considerable, is 

 now greatly intensified, for he is exceedingly jealous and takes of- 

 fense at every appearance of intrusion or even approach to the 

 domain which he ha^; appropriated for his own. The males, too, are 

 fewer than the females, and a consequence is that there are many 

 furious battles. Smitt tells what may happen : 



Two rivals rush with the speed of arrows against each other, deal a power- 

 ful side-stroke with their sharp ventral spines, and hasten with undiminished 

 speed each back to his own domain. After a few onsets the superiority of the 

 stronger combatant is demonstrated, his territory is extended, and he signal- 

 izes his triumph by a splendor of colours, while the Aanquished lays aside 

 his brilliant dress as though overcome by shame. While the males disport 

 themselves in these chivalrous tournaments, or rather, fight for their nests, the 

 females swim about in long troops of greater or less strength outside the battle 

 ground, and now and then a male selects his temporary mate from the company. 

 The female that heads the troop swims forward with rapid darts, followed by 

 the others, suddenly stops and assumes a vertical position, with head turned 

 toward the bottom. The othei's assemble round her and range themselves in 



