PLATE III. 



Fig. 1. Float of young Velella seen from above, ^ of an inch in length : //' groove in which the mnin 

 branch of the circulatory system passes from the fixed edge of the float to the base of the keel. 

 In this stage the keel is a slight ridge surmounting the single central chamljer: o'o'\ apertures 

 opening externally from the lifth and seventh chamber on the right, and from the second and 

 fourth on the left. 



Fig. 2. The same as Fig. 1, seen in profile, showing the central chamber round which are arranged, in an 

 irregular elliptical shape, the eight chambers of which the float, at this stage, is composed: tt. 

 so called air tubes attached to the lower side of the float; /, groove of main branch of circula- 

 tory system. 



Fig. 3. Float of a young Velella measuring f^ of an inch. Lettering as above; o"'o"', apertures open- 

 ing externally from the ninth and sixth chambers on the right and left. 



Fig. 4. Profile view of the float of a young Velella having eight chambers, measuring ^ of an inch in 

 length. Lettering as in Fig. 2. The keel, a', rises quite perceptibly above the central cham- 

 ber on a slight conical projection : cO—a^, successive chambers of the float. 



Fig. 5. Profile view of Fig. 3. Lettering as before. The keel has greatly increased in height and the 

 second line of growth is apparent. 



Fig. 6. Float of young Velella with twelve chambers measuring \ of an inch in length and having seven 

 lines of growth in the keel, which, in this stage, is a high conical lamella of entirely different 

 proportions to the float than in the adult or larger specimens. 



Fig. 7. Profile of central part of the float and keel of a young Velella with twelve chambers, but only 

 four lines of growth in the keel ; this .is also much broader than is usually the case at this 

 stage, — j*^" in length. 



Fig. 8. Profile of young Velella with seventeen chambers in the float, measuring ^^" in length, with six 

 lines of growth in the keel. 



Fig. 9. Portion of horizontal surface of the float of young Velella with twelve chambei-s, showing the 

 openings leading from one chamber to the adjoining ones through the common walls ; the 

 opening in the last chamber opens externally. 



Fig. 10. Showing on a somewhat larger scale the passages leading from one chamber to the other in the 

 eight outer chambers of the float of the preceding figure. 



Figs. 11, 12, 13. Opening in the outer chamber of three young Velellse varyuig in size from ^ to nearly -J 

 an inch in length. This opening is always in continuation of the line of openings forming the 

 communication between adjoining chambers. 



Fig. 15. Diagrammatic transverse section of yoimg Velella with twelve chambers, showing the position 

 of the keel a', the central chamber a, and the concentric chambers a^-a^'- with the groove/ for 

 the main branch of the circulatory system. 



Fig. 16. Diagrammatic section of the float of a Velella with twenty-two chambers. 



Fig. 17. The corresponding section of the opposite side showing the position of the groove/. This groove 

 is only a fold of the upper walls of the chambers, and does not divide the chambers into dis- 

 tinct spaces ; they form each a continuous ring. 



Fig. 18. General view of the position of the clusters of tubides arising from the lower side of the four 

 inner chambers ; some of the tubules branch, a rare occurrence in our Velella. 



Fig. 19, Inner view of the conical part of the float of a large Velella, showing the position of the tubules 

 and the corrugations and folds of the lower walls of the inner chambers; the corrugations ccc 

 become less prominent in proportion to the distance from the central chamber ; near the mar- 

 gin of the float the walls merely bulge out and form slight undulations. 



Fig. 20. Tubules of a large Velella which have penetrated through the so-called liver, and appear on the 

 top of the liver when seen from the lower side of the cone of the float. 



Fig. 21. View from the inside of the central part of the float showmg the tubules of a young VeleUa 

 measuring about \" in length. 



Fig. 22. Basal part of three tubule.'^ near the attachment to the central chamber in a Velella measuring 

 about \ an inch in length. 



