22 DEVELOPMENT OF THE SQUID. 



Fig. 8. View of the left side of the same embryo. Reference letters as in figs. 6 and 7. 

 Fig. 9. Foreshortened dorsal view of the posterior surface of the embryo shown in plate 2, figure 10. 

 a, y, s, and m, as in the preceding figures; es, eye stalk, ^; gills; er, otocysts; si, inner siphon folds. 



Plate II. 



The letters of reference have the following significance in all the figures of this plate ; a, arms ; a', jsos- 

 terior or siphonal pair of arms; a", second pair; a'", third pair; e, eyes; er, otocyst ; es, eye stalk;/", 

 fins; ff, gills; /t, branchial hearts; m, mantle; mo, mouth; re, rectum; si, inner siphon folds; si', 

 lateral siphon folds; sm, siphonal muscle; v, velum; y, yolk; y', external yolk sac; y", yolk mass of 

 the eye stalks and head ; y'", and y"", yolk masses of the body and mantle. 



Fig. 10. Embryo a little older than the one shown in figures 7 and 8, represented with its dorsal surface 

 above, and showing the anterior surface of the body, as seen from the left side. 



Fig. 11. The posterior surface of an older embryo with its dorsal surface above. 



Fig. 12. A similar view of an older embryo, with its dorsal surface below. 



Fig. 13. An older embryo in the position of figure 12. In this and the following figures, only a small 

 portion of the external yolk sac, y', is represented. 



Fi"-. 14. The posterior surface of an older embryo, as seen from the right side, with the dorsal surface 

 below. 



Plate III. 



Fie. 15. A somewhat older embryo seen fi"om the right side. The external yolk is now so large that 

 only part of it is shown in the figure ; «', a", a'", a"", the four arms of the right side ; /, the fin ; g, the 

 gill ; n, the branchial heart ; m, the free edge of the mantle ; nc, the neck cartilage ; si, the siphon tube ; si', 

 the lateral chamber of the siphon ; u, the valve of the siphon ; x, the space between the integument and the 

 surface of the external yolk ; y', y'', y'", y"", the four divisions or regions of the yolk. 



Fig. 16. Posterior surface of a somewhat older embryo; e, eye; i, ink bag; r, rectum. The other 

 letters as in figure 15. 



Fif. 17. A free swimming sqnid with the external yolk almost absorbed. The letters as in the preceding 

 figures. 



Fir'. 18. A free swimming squid with the external yolk entirely absorbed. The letters as in the pre- 

 ceding figures. 



Fig. 19. Diagrammatic view of the right side of a Pulmonate embryo, with its dorsal surface above ; 

 y, foot ; A, neck region ; m, mouth ; ma, mantle ; c, foot-sinus ; r, rectum ; sa, shell area ; sh, shell ; 

 t, tentacle ; v, velum. 



Fi"-. 20. Diagrammatic view of the left side of a squid embryo, at the stage shown in figure 10 ; a, a, a, 

 arms ; c, sinus space around the yolk sac ; e, eye ; /, integument of yolk sac ; g, gill ; m, mouth ; ma, 

 mantle ; v, velum ; r, rectum ; s, inner siphon fold ; s', outer siphon fold ; t, eye-stalk ; y, yolk sac. 



