LIFE-HISTORY OF AMPHIGONOPTERUS AURORA. 195 



The foregoing table indicates clearly and the evidence has 

 been confirmed by the writer by a study of material obtained at 

 other localities that the smaller and younger females of Amphi- 

 gonoptcrus give birth to their young later in tJic season than do 

 the larger and older females. This is true likewise of Micro- 

 metnis miniums (Table II. ), and as Eigenmann (1894) has 

 demonstrated, of Cymatogaster and other genera of the family 

 (but Eigenmann made no definite age-determinations). This 

 delayed breeding of the smaller, younger females of AmpJiigonop- 

 terns and other Embiotocids may be an advantageous adaptation, 

 allowing the growth of the yearling females to be continued, as 

 the structure of the scales indicates it does, during the breeding 

 of the older females. Most of the females being one-year fishes 

 in Amphigonopterus at least, this added growth would seem to 

 admit of a material increase in the number of young produced. 



NUMBER OF YOUNG BORN BY FEMALES OF DIFFERENT 



SIZE AND AGE. 



/ 

 The following table III., based upon data obtained from 48 



breeding females of Amphigonopterus aurora (all obtained near 

 Piedras Blancas during the first week of June, 1916), conclusively 

 shows that the smaller females bear fewer young than do the older 

 and larger ones 



the one-year-old females with 5-9 young being 7694 mm. long 



(average length, 83 mm.) ; 

 the one-year-old females with 1015 young being 85-103 mm. 



long (average length, 96 mm.) ; 

 the 3- or 4-year-old females with 16-30 young being 121-129 mm. 



long (average length, 125 mm.). 



Exceptional cases, excluded from this summary, are those of a 

 three-year female with but 9 small young, and a one-year female 

 with 19 young. Dr. Eigenmann (1894) has similarly found that 

 the smaller females of several other species of the Embiotocidse 

 bear fewer young than do the larger ones, and the data presented 

 in Table II. shows that this holds true in the case of Micrometrus 

 minimus. 



