LIFE-HISTORY OF AMPHIGONOPTERUS AURORA. 191 



* 



than do the larger ones (as also in Micrometrus miniums and 

 other embiotocids) suggests that fertilization is delayed for a 

 considerable period subsequent to copulation. Now it is a well- 

 known fact, in oviparous as well as in viviparous fishes, that the 

 larger females of a given species are more prolific than smaller 

 ones, and that is the situation in this family. In the present in- 

 stance, however, it is presumed that the copulation preceding the 

 development of the first brood of young (those carried by the 

 yearling females under discussion) takes place soon after birth, 

 when there is little variation in size or age (see preceding sec- 

 tion). If fertilization were then immediately effected, some 

 rather anomalous method of fertilization, or of egg production or 

 resorption, would have to be postulated to explain why those 

 females which would be smaller at the end of pregnancy bear 

 fewer young than those females, which for some reason, early 

 birth or otherwise, are destined to be larger when their young 

 are ready for birth. But if it be assumed that fertilization is de- 

 layed for some time, until a considerable variation in size shall 

 have arisen, the bearing of the fewer young by the smaller year- 

 ling fishes becomes no longer such a special problem. 



6. Finally, the young males are sexually mature immediately 

 after birth (see preceding section), at a time when they are asso- 

 ciated only with the newly-born females, which apparently do not 

 bear young until the next breeding season, one year later. A 

 similar situation presumably holds in the cases of Micrometrus 

 minimus and Cymatogastcr aggrcgatus. 



EMBRYONIC DEVELOPMENT AND NATAL METAMORPHOSIS. 



The developing embryos of the Embiotocidse, in compensation 

 for the reduced amount of yolk in the relatively minute egg, de- 

 rive their nourishment almost entirely from the nutritive ovarian 

 fluid in which they are bathed. This fluid, as Eigenmann (1894, 

 etc.) determined, is circulated by the action of cilia through the 

 embryos. The portion of the alimentary canal in which absorp- 

 tion chiefly takes place is doubtless the hypertrophied hind-gut, 

 which in the embryos of Amphigonopterus and Micromctnts, as 

 of other genera of the family, is a wide but thin-walled tube 

 nearly filled with long, hollow, vascular villi. The respiration of 



