PLATE IV. 



Fig. 1. Profile view of the keel and float of small Velella, measuring about I inch in length: ca, outer 

 chamber of the float; a, one of the concentric chambers; I, so-called liver; p, folds of the man- 

 tle covering the keel extending from the canal at the base of the keel to the canal e at the 

 edge of the mantle. 

 Fig. 2. Small Velella, about ^ of an inch in length, (seen from above) showing the few ramifica- 

 tions of the so-called liver system, I, seen through the float; s, rudimentary keel; fl, free 

 edge of the mantle. 

 Fig. 3. Slightly more magiiitied view of a part of the edge of a young Velella, somewhat older than the 

 preceding figm-e: r, principal ramifications; v', secondary ramifications of the free edge of 

 the mantle. 

 Fig. 4. Portion of the edge of a small Velella, measuring /t of an inch in length: v", primary 

 ramifications; v', secondary branches; g, mai'ginal glands of the free edge of the mantle, seen 

 from above. 

 Fig. .5. Portion of the edge of a small Velella, slightly older than the preceding figure, in which the 



principal ramifications still extend to the free edge of the mantle. 

 Fig. (). Portion of the edge of the float of a small Velella, about in the same stage as the preceding 

 figure, with proportionally larger marginal glands, but shorter secondary ramifications, than in 

 Fig. 4. 

 Fig. 7. Portion of the edge of the mantle of a Velella measuring about one inch in length, with long 

 marginal glands g, with a simple free edge of the mantle e, extending beyond, and small 

 clusters of yellow cells c, moderately closely packed along the outer edge of the mantle. 

 Fig. 8. Portion of the edge of the mantle of a Velella, measuring about two inches in length, with a 

 fringed free edge of the mantle e, beyond the marginal glands g, with large patches of yellow 

 cells c, closely packed together over the whole of the free edge of the horizontal mantle hv- 

 yond the float. 

 Fig. 9. Somewhat more magnified view of a part of the horizontal mantle of the float, to show the shape 

 of the ramifications of the so-called liver canals extending between the patches of yellow cells. 

 Single cluster of yellow cells with the fan-shaped terminations of the liver canals. 

 Portion of the outer edge of the horizontal mantle of a Velella, in which the ramifications of the 



vascular system terminate in sacs more or less filled with clusters of yellow cells. 

 Separate clusters of terminal extremities of the vascular system of a Velella nearly in the stage 



of the preceding figure, taken near the edge of the float. 

 Pouch-like terminal clusters of the vascular system filled with yellow cells, seen from above near 



the glandular band of the mantle. 

 Shows the delicate dendritic ramifications of the large vascular (liver) canals seen from the 



lower side of the float, entirely free from accumulations of yellow cells. 

 Part of one of the main vascular tubes, with large star-shaped ramifications and large clusters of 

 yellow cells, seen from the ujjper surface, near the float. 



