SYNOPSIS. Certain aspects of development that are indicative of changing funct~onal and ecological capabilities are reviewed for six different organ systems in the northern an- chovy, En,qrnulL mor&, and other teleosts. The six organ svstems are the integument, the lateral line system, the eve, the digestive tract, the gas bladder. and the trunk mu+ culature. The integument develops graduallv hut also has transient bpecialized cells during the larval period. The lateral line svstem is functional at hatching and then elaborates h\ recruitment proportional to growth during the larval period. The eves are cnpahle of photopic hinocular vision when feeding starts, dnd hter gr-adually develop d xotoplc system. The digestive tract develops a capacity for protein digestion and tiltering during the mid and late larval period. The gas bladder graduallv develops an expansion capabtlitv hv muscle differentiation dfter initial inHation. The trunk musculature differentiatea and recruits two fiber types that gradually supercede the embrvonic musculature during the larval period. Thus much of the development of organs in the anchovy after hatchinq or after feeding starts can be characterized as initial differentiation and then continued recruitment of specialized cell arrays. Behavior patterns appear to develop in conjunction with wch reci-tiitments. Th15 may apply to fishes generally, hut pattern and tempo (it development must differ among species. Brief comparison of the anchovy and the Pacitic in;tckerel. which has a more rapid md direct development. suggests that wine ot the differences in the two tvpea (it Iiirvae relate to the marked difference in teeding inodes of the adult stages.