DEVELOPMENT OF CUTTLE-FISHES. 



279 



and a day later the rudiments of the ears, of the pharynx 

 and salivary glands ; while a day or two after, the ventri- 

 cle, auricles, the kidneys, the ink-sac, and liver develop. 

 Contrary to the usual rule the ganglia arise from the middle 

 instead of the outer germ-layer. After this the germ grad- 

 ually develops until it rises above the surface of the egg, 

 and soon the yolk is partly absorbed and is contained in a 



FIG. 217. 



FIG. 218. 



Fig. 217. Embryo of Loligo Pealii. a, a", a'", a"", the right arms belonging to 

 four pairs ; e, the side of the head ; e, the eye ; /, the caudal fins ; /*, the heart ; m, 

 the mantle in which the color- vesicles are already developed and capable of chang- 

 ing their colors ; o, the internal cavity of the ears ; s, siphon. After Verrill. 



Fig. 218. The same as Fig. 217, but more advanced. The lettering in Figs. 217 and 

 218 the same. Both after Verall. 



large yolk sac, as in Figs. 217, 218. Finally the young cut- 

 tle-fish hatches in the form indicated by Fig. 219, and then 

 swims free upon the surface of the sea. 



The development of Cephalopoda in general is, then, di- 

 rect, i.e., there is no metamorphosis, the phases of meta- 

 morphosis seen in most other mollusks not appearing ; but 

 in an unknown species of cuttle-fish whose eggs were found 

 floating on the Atlantic, the germ, after the partial segment- 

 ation of the yolk, assumed a trochosphere condition (Fig. 220) 

 before the definitive features (Fig. 221) of the cuttle-fish 



