450 PARENTAL CARE AMONG FRESH-WATER FISHES. 



nearly symmetrical pair, and eggs are existent or developed in abont 

 three sets. According to Wyman, the eggs •■' are arranged in three 

 zones corresponding to three successive broods, and probably to be 

 discharged in three successive years. In the female of one species, 

 18 inches long, the mature eggs measured " three-fourths of an inch in 

 diameter '' and those of the second zone " one-fourth," while those 

 of the third were very minute — " about one-sixteenth of an inch." 

 Turner found in an Indian fish that the largest eggs were about as 

 large as '' grapes or small cherries," those of the second series " like 

 medium-sized shot," and the smallest " like minute granules." The 

 size of the eggs varies more or less with the species and perhaps with 

 the average size of the species. Those of the common large bagre of the 

 Argentine Republic {Netnma barhvs or co'm,m,ersonii)^ have a diam- 

 eter of 17 or 18 millimeters (three-fourths of an inch). 



The number of mature eggs differs considerably, but, as would 

 naturally be expected, are never in large number, as fishes' eggs go. 

 Wyman found " between twenty and thirty " in the mouth of each 

 male he observed, Turner found twelve in one of his females, 

 while in the mouth of one male he found ten and from that of an- 

 other " thirteen were shaken out." In the opinion of Turner, and 

 apparently of Wyman, " a close relation exists between the number 

 of eggs which come to maturity at a given time and the number 

 which the male can carry in his mouth." 



According to Day, however, " in the' female organs of generation 

 the eggs seem to come to maturity in batches of perhaps fifty at a 

 time," but he " found many males of the genus " Ariiis or Tachisurus, 

 '' and also of Osteogeniosiis^ with from fifteen to twenty eggs in their 

 mouths." This concatenation certainly requires verification. Doubt- 

 less the number of eggs matured varies with size as well as species. 



It may be also that the number of eggs in the mouth of a male may 

 be no certain criterion of the number in a given female. Wyman, 

 for instance, " in the mass of eggs with Avhich the mouth " was filled, 

 " occasionally found the eggs, rarely more than one or two, of an- 

 other species." The only way, he thought, in Avhich the presence of 

 the exceptional eggs could be accounted for '' is by the supposition 

 that while feeding the eggs are disgorged, and as these fishes are 

 gregarious in their habits, Avhen the ova ai'e recovered the stray Qgg 

 of another species may be introduced into the mouth among those 

 which naturally belong there." It is, however, improbable that the 

 male feeds while the eggs are benig hatched or that he disgorges 

 them. 



In some cases, at least, special provision appears to be made by the 

 female to receive the emitted eggs. Day found, " on examining the 



<^ Arius commersonii of most authors. 



