320 A. E. Yerrill — North American Cephalopods. 



11th of June, in the vicinity of New Haven, many of these eggs con- 

 tain embryos in a(lvanced stages of development (PLite XLI, figs. 2, 

 3 ; Plate XLV, fig. 4). The embryos, before hatching, can swim 

 around inside the eggs. 



These embryos are very beautiful objects to observe under the 

 microscope. 



Even at this early period some of the chromatophores are already 

 developed in the mantle and arms, and during life, if examined under 

 the microscope, these orange and purple vesicles can be seen to con- 

 tract and expand rapidly and change colors, as in the adult, but the 

 phenomena can be i'ar more clearly seen in these embryos ovring to 

 the greater transparency of the skin. In the young the chromato- 

 phores are very regularly and symmetrically arranged, on the arms, 

 head, and mantle. At this stage of development the eyes are brown. 

 In these embryos a remnant of the yolk-sac {y), appears to protrude 

 from the mouth, but it is really connected with the space around 

 the mouth and pharynx, and into this it is eventually absorbed. 



The more advanced of the embryos were capable of swimming 

 aboiit, when removed from the eggs, by means of the jets of water 

 from the siphon (s), which is developed at an earlier stage. The 

 arms {a"-a"") are then short, blunt, very unequal, with few minute 

 suckers ; the dorsal arms are very small, while those of the 2d and 

 3d pairs are successively longer, and have distinct suckers; the ten- 

 tacular arms (a'") are longer and larger than any of the others, and 

 have larger suckei's, which already, in some examples, can be seen to 

 form four rows; the ventral arms (a"",) are about as long as the 2d 

 pair, and bear several suckers. The mantle {m) is short, and the 

 caudal fins (./') are very small, short, lateral, and sejDarately attached 

 to each side of the blunt posterior end of the body, thus recalling 

 their adult condition in Rossia. The eyes (e) are large and promi- 

 nent ; the rudimentary beak [d) and odontophore (I) are distinctly 

 visible. The two otoliths (o) are very distinctly visible, as highly 

 refracting ovate bodies, above the basal part of the siphon, one on 

 each side. The ink-sac (i), attached to the rectum (/), is conspicuous 

 on account of its dark color ; the gills {g) are provided with a small 

 number of transverse processes ; the heart (A) and the branchial 

 auricles (A' h') are easily seen, while they continue to pulsate. The 

 pen exists only in a rudimentary condition, as a thin cartilage. 



During July and August the young (fig. 5) from less than a 

 quarter of an inch to an inch or more in length, swim free at the 

 surface, and may often be taken in immense quantities with towing 



