DEVELOPMENT OF THE SQUID. 15 



The figures of the later stages hardly call for much descriptiou, since they show 

 sufficiently well in themselves the gradual change of shape, and the approximation to 

 the form and structure of the adult. 



Fig. 16 is a posterior view of an embryo a little older than the one shown in 

 fig. 15. A large rounded prominence on each side of the bed marks the position of 

 the eye-stalk, and the eyes are farther forward than they are in older specimens, but in 

 other respects the form is very similar to that of the adult. The ink sac, i, has appeared, 

 and is filled with ink, and the tip of the free portion of the rectum is prolonged at its 

 corners into the pair of ear-like anal valves. 



Figs. 17, 18, are copies of drawings made at Mr. Agassiz's laboratory at Newport during 

 the summer of 1876, from specimens which were found swimming at the surface of the 

 water of Narragansett Bay. As the arrangement of the chromatophores is like that of the 

 other embryos, they undoubtedly belong to the same species and are given here to show 

 the later stages of development. The external yolk-sac has almost disappeared in fig. 17, 

 and it is entirely wanting in fig. 18. 



There are considerable individual variations in the arrangement of the chromatophores, 

 but there are certain features which were observed in all the specimens, and which seem 

 to be constant. 



The first which make their appearance are dark brown in color, and are placed 

 in a ring of six or seven (plate 2, fig. 14), around the edge of the mantle on the posterior 

 surface. They are a little smaller, and somewhat more excitable than those which appear 

 subsequently, and they can be readily recognized in the later stages shown in figs. 15, 16, 

 17, 18. They are soon followed by larger spots of the same dark brown color, scattered 

 irregularly over the posterior surface of the mantle (fig. 16). 



The next spots to appear are upon the arms, and are also dark brown. At first 

 there are two upon the first or siphonal pair of arms, and three upon the second 

 pair (fig. 16). A fourth soon appears upon the second arm, and these four remain 

 conspicuous until quite a late stage of. development (fig. 18). Three large brown spots 

 now appear upon the posterior surface of the head (fig. 16), and they are soon followed by 

 others (fig. 17). 



A second set of spots, more deep-seated and of a bright orange color, soon make their 

 appearance, and are much more constant in position than the brown ones. The first pair 

 which appear are just in front of, or ventral to the eyes. They are soon followed by a 

 single one on the middle Hne of the head, at the bases of the first pair of arms, and 

 another single one oil the middle line of the edge of the mantle. About the same time 

 a pair appear dorsally to the eyes, and another pair on the edge of the mantle, near 

 the sides. 



Four small orange spots next appear upon the second pair of arms (fig. 17, a"), 

 alternating with the four larger brown spots, and soon after a ring of six or eight orano-e 

 spots appears on the mantle, dorsal to the ink bag. Two orange spots next appear 

 upon the first pair of arms, figure 18, a', alternating with the brown spots. 



I was not able to procure specimens in sufficient numbers to follow the development of 

 the spots to any later stage than this, but they do not seem to develop regularly at the 

 later stages. 



