288 PROCEEDINGS OF THE AMERICAN ACADEMY 



extent in young Lumpus measuring 34""™ in length (Plate V. figs. 

 3, 4) : a line commencing to form along the anterior slope of the 

 anterior dorsal, a less prominent horizontal row on a level with the 

 line of the orbits close to the eyes, a thii-d lateral one along the body 

 at the level of the upper extremity of the operculum. This, the most 

 prominent of the rows, consisted of large, elliptical protuberances, 

 through which spiny processes projected (Plate V. figs. 3 a, 3 ^), and 

 a last row of somewhat smaller tubercles along the median line of 

 the abdomen behind the ventrals. The anterior dorsal fins of these 

 young stages (Plate V. figs. 3, 4) resemble greatly such permanent 

 anterior dorsals as exist in Chironectes, for instance. 



In the older stages (Plate V. figs. 1-4) the anterior dorsal has 

 become well separated from the posterior, the median fins are entirely 

 isolated, with well-developed fin rays, and the caudal has become sym- 

 metrical. The pectorals are somewhat larger, but otherwise they and 

 the ventral fin disks (Plate V. fig. 3 c) do not differ much from their 

 condition in younger stages. The early development of the pectorals 

 seems a marked characteristic of all embryos of osseous Fishes. 



These young stages of Lumpus were all collected close to the 

 shore ; they were found living among the eel-grass at Nahant, near 

 low-water mark. Giinther has figured"^ the young of Cyclopterus 

 spinosus. Of these stages, the youngest correspond to the oldest 

 stage of Cyclopterus lumpus here figured, the oldest measuring over 

 45nim iji length. 



Gasterosteus aculeatus, Lin, 



(Plate IX.) 



The changes due to growth in Gasterosteus closely resemble those 

 of Fundulus. The principal differences consist in the longer per- 

 sistence of the embryonic tail lobe, which* is still very prominent (Plate 

 IX. fig. 1) at a stage when in Fundulus the tail has become nearly 

 symmetrical. The notochord continues to extend into the tail as late 

 as the stage of Plate IX. fig. 4. The chromatophores are in the 

 shape of irregular spots during early stages ; they become more and 

 more dendritic as the young fish grow older (Plate IX. figs. 2, 3, 4). 

 In the stage of fig. 4 they begin to assume the arrangement forming the 

 vertical bands of the adult, and in the oldest stage here figured (Plate 



* An Introduction to the Study of Fishes (1880), p. 485. 



